feat: Add support for !ignore tag and !reference/!reference-all scalar shorthand (spec v0.2.8-1)

[dsillman2000]

v0.2.8-1 Spec Compliance Update

This branch brings the library up to spec v0.2.8-1.

What changed

• Added full support for the !ignore tag, including parsing, pruning, and correct behavior inside referenced files.
• Ensured !ignore interacts correctly with !merge and !flatten, so ignored sequence items are dropped before merge/flatten evaluation.
• Added scalar shorthand support for both !reference and !reference-all.
  Example: !reference "service.yaml" and !reference-all "configs/*.yaml".
• Added a new unit test suite for !ignore and expanded reference tests to cover shorthand parsing/loading.
• Updated the README with !ignore, shorthand syntax examples, and VS Code yaml.customTags guidance.

Why it matters

• Hidden anchor sections such as .anchors: !ignore now work cleanly without leaking into resolved output.
• !ignore can now be used safely inside composition pipelines built from !merge and !flatten.
• The parser now matches the spec for both mapping and scalar forms of reference tags.
• Spec compliance is restored for the latest upstream scenarios.

Verification

• uv run pytest tests/ -> 72 passed
• make spec-test -> 127 scenarios passed

[Copilot]

Pull request overview

Updates yaml-reference to match spec v0.2.8-0 by adding the new !ignore composition tag and allowing scalar shorthand for !reference / !reference-all.

Changes:

• Add scalar shorthand parsing for !reference and !reference-all.
• Introduce !ignore tag support, plus a pruning pass during full resolution.
• Add unit tests for shorthand parsing/loading and new !ignore behavior; update README examples and VS Code tag config.

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 5 comments.

File	Description
yaml_reference/__init__.py	Adds scalar shorthand parsing, introduces Ignore + prune_ignores(), and wires pruning into the load pipeline
tests/unit/test_reference.py	Adds shorthand coverage for both parsing and full resolution
tests/unit/test_ignore.py	New unit test suite covering !ignore behaviors and pruning
README.md	Documents !ignore, shorthand syntax, and updates VS Code YAML customTags guidance

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[ryodine]

awesome!