[perf] Avoid re-parsing current file in RemoveUnusedPrivateClassConstantRector

[guillaume-sainthillier]

Problem

ClassConstManipulator::hasClassConstFetch() searches for constant fetches in every ancestor of the class, resolved through AstResolver::resolveClassFromClassReflection(). ClassReflection::getAncestors() includes the class itself. So for every file that has a private constant, the file currently being processed was parsed again and its PHPStan scope fully resolved again, only to look for self::FOO in a class Rector already has in memory. The AstResolver cache doesn't help, because each file is processed once.

In a profile of Rector running its own rector.php on part of src/, this single call path accounted for ~16% of total runtime.

Change

• ClassConstManipulator::hasClassConstFetch() now requires the ClassLike owning the constant, and searches only that in-memory class and the traits it uses. Parents and interfaces are no longer resolved, as a private constant cannot be fetched there. AstResolver is kept only for traits, since a trait method runs in the using class scope (covered by skip_used_in_trait.php.inc).
• RemoveUnusedPrivateClassConstantRector now subscribes to Class_/Enum_ so it can pass the class node. Unused constants are collected first and removed afterwards, so the result doesn't depend on declaration order (as before, when the search ran on the unchanged file from disk).

Benchmarks

Single process, --dry-run --clear-cache, local machine:

Workload	Before	After
Rector's own rector.php (all prepared sets) on src/ (510 files)	~22.5s wall	~20.3s wall (−10%)
This rule only, ~3,400 vendor files (symfony, doctrine, nette, phpunit, …), parallel	27.5s / 167 CPU-s	19.5s / 132 CPU-s (−29% wall)

Behavior

• On the 3,400-file corpus, the code change Rector produces is identical before and after.
• Only the reported change metadata differs: since the rule now runs on the class node, the JSON changes entry points to the class line, with one entry per class instead of one per constant.
• All existing fixtures pass unchanged. Full test suite: 5,016 tests OK.

[TomasVotruba]

Thanks, lets ship it 👍