fix: expand decimal and cross-kind edge coverage

[aryamantodkar]

Summary

Expand deterministic realizer coverage for DECIMAL and harden complete-span validation across the previously fixed kinds.

What changed

• Add a local DECIMAL parser with signed values, point/dot fractions, named scales, scientific notation, grouping and locale separators, Unicode spacing, suffix scales, and parenthesized negatives.
• Canonicalize decimal values for evaluation equivalence while keeping runtime output stable.
• Reject malformed decimals, repeated scales, incomplete scientific forms, and unrelated trailing text.
• Extend CARDINAL sign handling and prevent invalid zero aliases from entering candidate options.
• Tighten DATE validation for impossible calendar values, eras, Roman years, compact weekday/month forms, quarter syntax, and unrelated suffixes.
• Validate TIME timezone names and offsets; reject malformed meridiem, separators, prefixes, and suffixes.
• Preserve MONEY currency identity and complete-span behavior; reject repeated scales and unrelated suffixes.
• Add complete-span guards for delegated PHONE and ELECTRONIC parsing.
• Update README, coverage documentation, and public/integration tests.

Invariant

Realizers must consume the complete annotated span and emit only valid runtime candidates. Evaluation equivalence may ignore formatting and representation differences, but must preserve semantic identity such as numeric value, date/time value, and currency.

Validation

• uv run ruff format --check .
• uv run ruff check .
• uv run pytest (6 passed)
• cargo test --manifest-path rust/Cargo.toml (44 passed)
• uv build

Dataset evidence

The documented audits cover all available Google shards. Remaining mismatches are malformed, contradictory, or annotation-artifact rows rather than ordinary missing representations.

Target branch: epic/realizer-edge-cases.