[Caching] Keep cache on rule removal and skip addition

[TomasVotruba]

Today any change to any config parameter drops the whole cache, because FileHashComputer hashes every parameter through SimpleParameterProvider::hash(). So removing a rule from withRules(), adding a withSkip() item, or even flipping --parallel forces a full re-run.

This compares config changes by direction instead of a flat hash:

• removing a rule/set, or adding a skip -> strictly less work -> cache kept
• adding a rule/set, or removing a skip -> more work possible -> cache dropped
• output-affecting parameters (php version, import names, indent, ...) -> any change still drops the cache
• runtime/reporting parameters (parallel, memory limit, deprecation notices, unused-skip reporting) -> excluded, never invalidate

Behavior

 // rector.php
 return RectorConfig::configure()
     ->withRules([
         SomeRector::class,
-        OtherRector::class,
     ]);

Before: full cache dropped, every file re-analysed.
After: cache kept, only changed files re-analysed.

 return RectorConfig::configure()
     ->withSkip([
         SomeRector::class,
+        AnotherRector::class,
     ]);

Before: full cache dropped.
After: cache kept (adding a skip only removes work).

How

• SimpleParameterProvider::hashForCacheInvalidation() hashes only output-affecting parameters, leaving out the ignored and directionally compared ones.
• ChangedFilesDetector stores a small snapshot (strict hash + hashed rule/set/skip lists) and compares it directionally on the next run.
• A legacy string cache value from an older version triggers a single safe reset.

Note

A pre-existing gap, not changed here: a configured rule value change via withConfiguredRule() is stored on RectorConfig, not in the parameter bag, so it already does not invalidate the cache. Can be a follow-up if worth closing.