[kvlonge]

Why

Later native milestones need Rust building blocks that match Python exactly: identities and diagnostics, text positions, JSON text that equals json.dumps/orjson byte for byte, and configuration reading that matches tomllib and PyYAML. This PR adds those foundations only. Nothing is wired into the compile path, and Python behaviour does not change.

Changes

• sqlbuild-core: passive identity, diagnostic and SQL value types; LineIndex positions with Python universal-newline decoding; an exact json.dumps/orjson emitter. The orjson floor rises to 3.11.7, whose float layout it reproduces.
• New sqlbuild-config crate:
  • tomllib-compatible TOML (creation order, namespace rules, CRLF, TOML 1.1 rejection);
  • PyYAML-compatible YAML 1.1 (PyYAML's block scalar scanner, resolver and SafeConstructor);
  • typed project/local config readers.
• Contract: native either returns exactly Python's value or defers to Python.
  • YAML that SafeLoader and CSafeLoader read differently is deferred.
  • Alias, merge and nesting expansion are bounded, as are TOML depth and JSON depth/digits, so hostile input defers instead of crashing; large single-line collections load in linear time.
• Internal _oracle_* hooks (not an API) and seeded oracles:
  • JSON: 9 × 1500 values;
  • text positions;
  • YAML: 7000 documents vs both loaders;
  • TOML: 5000 general and 5000 namespace documents;
  • repository files;
  • hostile documents with a time bound.

Verification

• cargo test --workspace --all-features; clippy -D warnings and fmt on 1.98.0; make check-native-layering
• uv sync --all-extras --reinstall-package sqlbuild, then oracle tests and review repro scripts: no crash, no harmful mismatch
• 2.6M fuzzed YAML documents: zero accepts that differ from either loader
• 80k fuzzed TOML documents: zero wrong results
• make test (11204 passed), make check-ci, public-repository scanner