CoversClass does not transitively target traits used by enumerations

[no-simpler]

Problem

When a class uses a trait, #[CoversClass(TheClass::class)] transitively whitelists the trait's lines for coverage. When an enum uses the same trait, the trait's lines are not whitelisted — PHPUnit flags the test as risky:

This test executed code that is not listed as code to be covered or used: …

This forces authors to add #[UsesTrait] or #[CoversTrait] to enum tests, which is inconsistent with the class behavior and creates friction with static analysis tools that don't accept those attributes.

A minimal reproduction is available at https://github.com/no-simpler/phpunit-psalm-trit-catch22 (rows 1 vs 4 in its test matrix).

Root cause

CodeUnitFindingVisitor::leaveNode() resolves trait usages only for Class_ and Trait_ nodes. Enum_ extends ClassLike (not Class_), so it is excluded by the early-return gate. Enums are correctly discovered in enterNode() via processClass(), but their trait lists are never populated.

Changes

Three one-line fixes in CodeUnitFindingVisitor:

1. leaveNode() — include Enum_ in the gate so enums proceed to trait resolution
2. postProcessClassOrTrait() signature — widen the type union to accept Enum_
3. postProcessClassOrTrait() body — route Enum_ into the class branch (enums are stored in $this->classes)

Plus a regression test (testHandlesEnumUsingTrait) and fixture file mirroring the existing testHandlesTraitUsingTrait pattern.

Note: This is a copy of !1145, re-created on branch 12.5 to be able to merge as bug fix.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 88.21%. Comparing base (f3a1f87) to head (f6c3b9b).
⚠️ Report is 1 commits behind head on 12.5.
✅ All tests successful. No failed tests found.

Additional details and impacted files

@@            Coverage Diff            @@
##               12.5    #1147   +/-   ##
=========================================
  Coverage     88.21%   88.21%           
- Complexity     1398     1400    +2     
=========================================
  Files           105      105           
  Lines          4718     4718           
=========================================
  Hits           4162     4162           
  Misses          556      556           

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