Replace rector/type-perfect with tomasvotruba/type-coverage

[TomasVotruba]

The type-perfect rules have moved into tomasvotruba/type-coverage 2.3.0, which now ships them as a bundled package:

"extra": {
    "phpstan": {
        "includes": [
            "config/extension.neon",
            "packages/type-perfect/config/extension.neon"
        ]
    }
}

So rector/type-perfect is dropped and tomasvotruba/type-coverage added in its place.

 "require-dev": {
-    "rector/type-perfect": "^2.1",
+    "tomasvotruba/type-coverage": "^2.3",
 }

The type_perfect config key is unchanged, so phpstan.neon keeps its existing settings as-is - only the doc link is updated:

-    # see https://github.com/rectorphp/type-perfect/
+    # see https://github.com/TomasVotruba/type-coverage
     type_perfect:
         no_mixed: true
         null_over_false: true
         narrow_param: true
         narrow_return: true

Note: tomasvotruba/type-coverage 2.3 requires PHP ^8.4, one step above this package's "php": ">=8.3" runtime constraint. It is a require-dev only, and every CI job here already runs on 8.4 or 8.5, same as the existing tomasvotruba/unused-public dev dependency.

The type_coverage rules that come along in the same package report nothing here - the codebase is already above their default 99% thresholds.