Migrate integration and provider HTTP types (PR 13)

[prk-Jr]

Summary

• Replace the remaining Fastly request and response boundaries in the integration and auction provider layers so PR13 runs on platform-agnostic HTTP types.
• Move provider dispatch onto RuntimeServices HTTP client primitives with async request_bids, PlatformPendingRequest, and PlatformResponse while preserving orchestrator deadline handling.
• Finish the review hardening for Testlight response normalization and convert the migrated integration tests to HTTP-native fixtures.

Changes

File	Change
crates/trusted-server-adapter-fastly/src/main.rs	Route integration proxy requests through the HTTP-native registry boundary and pass RuntimeServices into the PR13 entrypoint.
crates/trusted-server-core/src/auction/README.md	Update provider guidance and examples to PlatformPendingRequest, PlatformResponse, and the platform HTTP client flow.
crates/trusted-server-core/src/auction/endpoints.rs	Thread RuntimeServices into the auction entrypoint context.
crates/trusted-server-core/src/auction/orchestrator.rs	Await async provider launches, operate on PlatformPendingRequest/select, and update the remaining PR13 migration comments.
crates/trusted-server-core/src/auction/provider.rs	Convert AuctionProvider to async request_bids with PlatformPendingRequest/PlatformResponse and refresh the trait docs.
crates/trusted-server-core/src/auction/types.rs	Add RuntimeServices to AuctionContext.
crates/trusted-server-core/src/integrations/adserver_mock.rs	Migrate the mock provider to platform HTTP pending/response types.
crates/trusted-server-core/src/integrations/aps.rs	Migrate APS provider request dispatch and response parsing to platform HTTP types.
crates/trusted-server-core/src/integrations/datadome.rs	Convert DataDome proxying to HTTP-native request/response handling via the platform client.
crates/trusted-server-core/src/integrations/didomi.rs	Convert Didomi proxying to HTTP-native request/response handling via the platform client.
crates/trusted-server-core/src/integrations/google_tag_manager.rs	Remove Fastly shims, keep bounded POST handling on HTTP bodies, and convert GTM tests to HTTP-native fixtures.
crates/trusted-server-core/src/integrations/gpt.rs	Remove Fastly request/response compat from GPT asset proxying and convert GPT tests to HTTP-native fixtures.
crates/trusted-server-core/src/integrations/lockr.rs	Convert Lockr SDK/API proxy handling to HTTP-native request/response types.
crates/trusted-server-core/src/integrations/permutive.rs	Convert Permutive SDK/API proxy handling to HTTP-native request/response types.
crates/trusted-server-core/src/integrations/prebid.rs	Move Prebid provider dispatch to async platform HTTP requests and parse PlatformResponse results.
crates/trusted-server-core/src/integrations/registry.rs	Migrate IntegrationProxy/routing types to http types and thread RuntimeServices through proxy dispatch.
crates/trusted-server-core/src/integrations/testlight.rs	Convert Testlight to HTTP-native request/response handling, add the stale Content-Length regression test, and drop stale length headers when rebuilding JSON responses.

Closes

Closes #494

Test plan

• cargo test --workspace
• cargo clippy --workspace --all-targets --all-features -- -D warnings
• cargo fmt --all -- --check
• JS tests: cd crates/js/lib && npx vitest run
• JS format: cd crates/js/lib && npm run format
• Docs format: cd docs && npm run format
• WASM build: cargo build --package trusted-server-adapter-fastly --release --target wasm32-wasip1
• Manual testing via fastly compute serve
• Other: cargo doc --no-deps --all-features (passes with pre-existing unrelated rustdoc warnings outside this PR's scope)

Checklist

• Changes follow CLAUDE.md conventions
• No unwrap() in production code — use expect("should ...")
• Uses repo-standard logging macros, not println!
• New code has tests
• No secrets or credentials committed

[ChristianPavilonis]

PR Review — Migrate integration and provider HTTP types (PR 13)

1 blocking finding, 5 non-blocking suggestions.

Blocking

🔧 Missing Content-Type forwarding for Didomi POST/PUT — see inline comment.

Non-blocking (inline)

• 🤔 Prebid still imports from fastly::http — last remaining use fastly in the integration layer
• ♻️ Duplicated body collection helpers (collect_response_body / collect_body_bytes)
• 🌱 Unbounded response body collection (matches pre-migration, but could use a size cap)
• ⛏ Dead "X-" uppercase branch in custom header copy (http crate lowercases names)
• ⛏ Duplicated backend_name_for_url helper across 4 integrations