feat: generate request construction to avoid reflection pipeline

[glennawatson]

What kind of change does this PR introduce?

Feature

What is the new behavior?

This PR adds the generation 2 request-building path for Refit source-generated clients. When RefitGeneratedRequestBuilding is enabled, eligible generated methods no longer route through the reflective runtime request-builder path. Instead, the generator emits the request construction directly into the generated client method:

• creates HttpRequestMessage instances in generated code
• emits static method headers, dynamic [Header] parameters, and [HeaderCollection] handling
• emits [Body] serialization setup and buffering/streaming behavior
• emits [Property] parameters and interface property values into request options/properties
• emits cancellation token plumbing, API response handling, void response handling, and response disposal behavior
• dispatches through the new GeneratedRequestRunner runtime helper instead of building an invocation delegate through BuildRestResultFuncForMethod

The opt-in keeps the existing reflective path as the default and preserves fallback behavior for request shapes that are not safe to generate inline yet. The tests explicitly assert both sides: switch-off output still uses the reflective builder, while switch-on output avoids it for supported methods.

The generator itself is reworked around the new request model used by this path:

• introduces request-specific parser and model types for request parameters, headers, body buffering, interface properties, and method request generation
• keeps Roslyn 4.8 and Roslyn 5 generator packages using the same shared generator implementation
• replaces the old shared-project/projitems wiring with SDK-style globbing for the shared generator sources
• gives the incremental generator combine stages named helper records instead of opaque nested tuple access
• updates generated output emission to share helper code and produce the new generated request-building call sites

The runtime receives the support surface needed by the generated code:

• adds GeneratedRequestRunner as the shared runtime implementation for generated request sending, body content creation, header application, configured request options, and typed request properties
• exposes RefitGeneratedRequestBuilding as a compiler-visible MSBuild property with a default of false
• updates public API baselines for the new generated-runner surface
• switches cache key hashing to HashCode and adds framework polyfills for HashCode, Index, and Range
• keeps old target framework support compiling by aligning generator/runtime polyfills with compiler-required members such as Index.GetOffset

The test layout is also updated:

• moves source-generation tests out of Refit.Tests into Refit.GeneratorTests
• adds generated request-building coverage for headers, header collections, body serialization metadata, typed properties, interface properties, inherited properties, and fallback behavior
• adds live compilation coverage that emits, loads, instantiates, and invokes a generated client using the inline request path
• updates the generator fixture to compile generated output against the trusted platform assembly closure so CI hosts include type-forwarded framework assemblies
• refreshes generated source snapshots for the new generator shape

What is the current behavior?

Generated Refit clients currently call into BuildRestResultFuncForMethod and pass an object[] argument array to the runtime request builder. That path depends on runtime method metadata lookup and request-building infrastructure even when the generator has enough information to emit the request construction directly.

The source generator implementation is also still wired through the older shared-project/projitems setup, and source-generation tests are mixed into the main runtime test project.

What might this PR break?

The generated request-building path is opt-in and defaults to off, so existing generated clients should continue using the current reflective request-builder path unless a consumer enables RefitGeneratedRequestBuilding.

The PR does add a new public-but-editor-hidden runtime helper surface for generated code and updates public API baselines accordingly. Generated source snapshots change because the generator implementation and emitted helper wiring changed.

Checklist

• I have read the Contribute guide
• Tests have been added or updated (for bug fixes / features)
• Docs have been added or updated (for bug fixes / features)
• Changes target the main branch
• PR title follows Conventional Commits

Additional information

Validation run locally:

• dotnet build src/Refit.slnx -c Release -v:minimal --no-restore
• dotnet build src/tests/Refit.GeneratorTests/Refit.GeneratorTests.csproj -c Release -f net8.0 -v:minimal --no-restore
• src/tests/Refit.GeneratorTests/bin/Release/net8.0/Refit.GeneratorTests
• src/tests/Refit.Tests/bin/Release/net8.0/Refit.Tests

[codecov]

Codecov Report

❌ Patch coverage is 97.56824% with 49 lines in your changes missing coverage. Please review.
✅ Project coverage is 97.49%. Comparing base (c7c14b4) to head (2bcfc7d).

Files with missing lines	Patch %	Lines
...rc/InterfaceStubGenerator.Shared/Parser.Request.cs	96.61%	0 Missing and 9 partials ⚠️
...rc/InterfaceStubGenerator.Shared/Parser.Helpers.cs	75.00%	3 Missing and 4 partials ⚠️
...it/RequestBuilderImplementation.QueryAndHeaders.cs	90.76%	3 Missing and 3 partials ⚠️
...stBuilderImplementation.QueryAndHeaders.Helpers.cs	89.74%	2 Missing and 2 partials ⚠️
src/InterfaceStubGenerator.Shared/Emitter.cs	99.04%	0 Missing and 3 partials ⚠️
...faceStubGenerator.Shared/Parser.Request.Helpers.cs	96.20%	1 Missing and 2 partials ⚠️
...c/Refit.HttpClientFactory/HttpClientFactoryCore.cs	83.33%	1 Missing and 2 partials ⚠️
src/Refit/RequestBuilderImplementation.cs	93.47%	1 Missing and 2 partials ⚠️
...aceStubGenerator.Shared/ImmutableEquatableArray.cs	93.33%	1 Missing and 1 partial ⚠️
src/InterfaceStubGenerator.Shared/Parser.cs	98.26%	0 Missing and 2 partials ⚠️
... and 6 more

Additional details and impacted files

@@             Coverage Diff             @@
##             main    #2150       +/-   ##
===========================================
+ Coverage   78.17%   97.49%   +19.32%     
===========================================
  Files          97      105        +8     
  Lines        3821     4711      +890     
  Branches      715      845      +130     
===========================================
+ Hits         2987     4593     +1606     
+ Misses        690       31      -659     
+ Partials      144       87       -57     

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[sonarqubecloud]

Quality Gate passed

Issues
2 New issues
0 Accepted issues

Measures
0 Security Hotspots
96.5% Coverage on New Code
1.6% Duplication on New Code

See analysis details on SonarQube Cloud