Share the method's runtime cache with fake closures of the same scope

[staabm]

disclaimer: this change was generated by claude opus. I have little experience with php-src development

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Creating a fake closure (Closure::fromCallable(), first-class callable syntax, ReflectionMethod::getClosure()) over a method whose runtime cache was not yet initialized allocated a cold per-closure heap cache on every creation. Initialize the method's own shared cache instead - exactly what the first real call would do - so repeated closure creations reuse one warm cache. Trampolines and heap-cache functions keep the per-closure path.

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after this PR

➜  php-src git:(closure) ✗ hyperfine 'sapi/cli/php -n -d opcache.enable_cli=0 closure_from_callable_runtime_cache_bench.php'
Benchmark 1: sapi/cli/php -n -d opcache.enable_cli=0 closure_from_callable_runtime_cache_bench.php
  Time (mean ± σ):     136.5 ms ±   1.4 ms    [User: 132.8 ms, System: 2.3 ms]
  Range (min … max):   133.4 ms … 138.7 ms    21 runs

before this PR

➜  php-src git:(closure) ✗ hyperfine 'sapi/cli/php_old -n -d opcache.enable_cli=0 closure_from_callable_runtime_cache_bench.php'
Benchmark 1: sapi/cli/php_old -n -d opcache.enable_cli=0 closure_from_callable_runtime_cache_bench.php
  Time (mean ± σ):     150.6 ms ±   1.3 ms    [User: 147.2 ms, System: 2.3 ms]
  Range (min … max):   148.3 ms … 152.9 ms    19 runs

benchmark closure_from_callable_runtime_cache_bench.php: https://gist.github.com/staabm/20c082674ed880c8fc097b4775f2d7a7