Remember function return type extensions

[staabm]

before this PR:

➜  phpstan-src git:(2.1.x) ✗ PHPSTAN_GNSR=1 hyperfine 'php vendor/bin/phpunit tests/PHPStan/Analyser/NodeScopeResolverTest.php' --runs=5
Benchmark 1: php vendor/bin/phpunit tests/PHPStan/Analyser/NodeScopeResolverTest.php
  Time (mean ± σ):     15.219 s ±  0.105 s    [User: 14.850 s, System: 0.359 s]
  Range (min … max):   15.059 s … 15.339 s    5 runs

---

after this PR:

➜  phpstan-src git:(remember-fns) ✗ PHPSTAN_GNSR=1 hyperfine 'php vendor/bin/phpunit tests/PHPStan/Analyser/NodeScopeResolverTest.php' --runs=5
Benchmark 1: php vendor/bin/phpunit tests/PHPStan/Analyser/NodeScopeResolverTest.php
  Time (mean ± σ):     15.049 s ±  0.230 s    [User: 14.679 s, System: 0.360 s]
  Range (min … max):   14.659 s … 15.264 s    5 runs

[staabm]

interessting.. I don't see this errors locally.. will have another look

[phpstan-bot]

This pull request has been marked as ready for review.