feature - implement RFC 022 format functions (#39)

[dannymeijer]

Summary

• completes RFC 022's scalar format-function surface: deterministic hashes, URL helpers, JSON payload helpers, and CSV payload helpers
• adds registry-backed helpers and Substrait extension mappings for concrete format helpers, with sha2(...) kept as a compatibility rewrite over concrete SHA-2 helpers
• executes the full format helper set through the DataFusion adapter using native DataFusion functions where available and Incan-authored UDF callbacks for non-native helpers
• removes the package-local Rust inql-datafusion-format adapter crate; the remaining adapter logic is Incan source using Rust bridge imports only where needed
• records dynamic variant predicates as reserved/rejected until InQL has a variant value model, instead of exposing fake string predicates
• marks RFC 022 Implemented and updates format reference docs, release notes, and the RFC index

Type of change

• Bug fix
• New feature
• Refactor / maintenance
• Documentation
• RFC (adds/updates docs/rfcs/*)

Area(s)

• Package & tests
• Specification (RFCs)
• Documentation
• Automation & repo config
• Other

Key details

• User-facing behavior: Authors can use hash helpers (md5, sha1, concrete SHA-2 helpers, sha2, crc32, xxhash64), URL parse/encode/decode helpers, JSON validation/path/schema helpers, and CSV row/schema helpers in scalar projections.
• Internals: Concrete helpers declare registry-owned Substrait extension mappings. DataFusion support is adapter-owned, but implemented in Incan source through src/session/datafusion_format_functions.incn rather than a package-local Rust crate.
• Boundary: Dynamic variant predicates such as typeof, is_array, and is_object remain unavailable until a variant value model exists.
• Compiler baseline: This branch expects Incan 0.3.0-rc23, which includes the Rust bridge callback/type-alias fixes needed by the Incan-authored DataFusion UDF bridge.

Testing / verification

Verified with Incan 0.3.0-rc23 candidate:

• make fmt
• git diff --check
• incan test tests/test_hashing_functions.incn
• incan test tests/test_format_functions.incn
• incan test tests/test_function_registry.incn
• incan test tests/test_substrait_plan.incn
• incan test tests/test_session_projection.incn
• make fmt-check
• make test-style
• make registry-metadata
• make build
• make build-locked
• make test
• make smoke-consumer
• make pre-commit

Note: make registry-metadata still prints the known incan.lock is out of date warning for its package-root metadata command, but the command passes and make build-locked passes against the refreshed lockfile.

Docs impact

• No docs changes needed
• Docs updated

Links: docs/language/reference/functions/format.md, docs/language/reference/functions/index.md, docs/release_notes/v0_1.md, docs/rfcs/022_semi_structured_format_functions.md, docs/rfcs/README.md

Stack / Merge Order

Merge after Incan 0.3.0-rc23 is available on InQL CI's release/v0.3 checkout. This PR is full RFC 022 scope and closes #39.

Refs #39
Refs dannys-code-corner/incan#708
Refs dannys-code-corner/incan#709