chore: release v1.5.2

[theodevelop]

Summary

Aggregated PR for v1.5.2 — four false-positive fixes from issue #38 (discovered
while testing against a real-world Flex file) and one new feature (#39).

Changes

Fixed (#38)

• SC refs in multi-line block headers: <SC_A,\nSC_B,\nSC_C>{ only recorded
  the closing SC; all others had 0 refs → false flex/unused-sc and wrong Code Lens counts.
• Abbrev refs on indented rule lines: {ABBR} inside an indented <SC>{ } block
  was not counted as an abbreviation reference → false flex/unused-abbrev.
• Transitive abbreviation references: abbreviations used only inside another
  abbreviation's definition (e.g. ALNUM {ALNUM_Q}|{ALNUM_A}) were never recorded
  as referenced → false flex/unused-abbrev for the inner abbreviations.
• flex/unreachable-rule false positive for complex patterns: isWordPattern
  classified [A-Z]+(\.[A-Z]+)+ (requires a literal dot) as a general identifier
  pattern, producing false shadowing warnings for keyword rules that followed it.

Added (#39)

• Code Lens for Flex abbreviations: abbreviation definitions now show a clickable
  "N references" lens, consistent with start conditions and Bison rules.

Tests

• 356 parser tests, 211 diagnostic-code tests — 0 failed.

Checklist

• npm run compile clean
• All test suites pass
• CHANGELOG.md updated
• package.json version bumped to 1.5.2