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
• exposes explicit-schema JSON/CSV helpers through Incan model type parameters, e.g. from_json[Payload](...) and from_csv[Row](...)
• 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.
• Model-derived schemas: from_json[T](...), try_from_json[T](...), and from_csv[T](...) derive schema metadata from compiler-provided Incan model/class type reflection. The public API uses the model type parameter directly, not schema strings, dummy model values, or schema wrapper helpers.
• 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-rc28, which includes the generic decorated type-parameter reflection and Rust string-boundary fixes needed by the model-typed JSON/CSV helpers.

Testing / verification

Verified locally with Incan 0.3.0-rc28 from merged release/v0.3:

• cargo build --bin incan in /Users/danny/Development/encero/incan
• make test INCAN=/Users/danny/Development/encero/incan/target/debug/incan
• make fmt-check INCAN=/Users/danny/Development/encero/incan/target/debug/incan
• make test-style INCAN=/Users/danny/Development/encero/incan/target/debug/incan
• make registry-metadata INCAN=/Users/danny/Development/encero/incan/target/debug/incan
• make build INCAN=/Users/danny/Development/encero/incan/target/debug/incan
• make smoke-consumer INCAN=/Users/danny/Development/encero/incan/target/debug/incan
• git diff --check

Notes:

• make test passed 175 package tests.
• make registry-metadata passed with 130 helpers and still prints the known incan.lock is out of date package-root warning.
• The first sandboxed make smoke-consumer attempt failed because DNS could not resolve index.crates.io; rerunning the same command with network access passed.

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

Incan 0.3.0-rc28 is merged on release/v0.3; this PR is now unblocked by the compiler fixes. This PR is full RFC 022 scope and closes #39.

Refs #39
Refs dannys-code-corner/incan#708
Refs dannys-code-corner/incan#709
Refs dannys-code-corner/incan#714
Refs dannys-code-corner/incan#715
Refs dannys-code-corner/incan#716