Validate named values in candidate parser

[thecrypticace]

Fixes tailwindlabs/tailwindcss-intellisense#1506

[coderabbitai]

Walkthrough

Adds a validation regex IS_VALID_NAMED_VALUE and applies it to named-value parsing paths in parseCandidate, parseModifier, and parseVariant, causing invalid named values to be rejected early or skipped. Test coverage is extended with three additional invalid named-value candidates. No public API or exported signatures were changed; only parsing behavior and tests were modified.

Pre-merge checks

✅ Passed checks (4 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title accurately summarizes the main change: introducing validation for named values in the candidate parser to fix invalid syntax handling.
Description check	✅ Passed	The description provides a reference to the linked issue that this PR addresses, relating to invalid named values in candidate parsing.
Linked Issues check	✅ Passed	The PR implements validation of named values in the candidate parser to detect and prevent reporting of invalid arbitrary-variant-with-value syntax like 'data-hovered=true:text-red-500', addressing issue #1506's core objective.
Out of Scope Changes check	✅ Passed	All changes are directly scoped to validation of named values in the candidate parser and related test coverage, with no unrelated modifications detected.

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• CHANGELOG.md (1 hunks)

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• CHANGELOG.md

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