php-in-php: VmMemory RSS — remove host getrusage() fallback (#7287)

[PurHur]

Summary

• Remove function_exists('getrusage') / getrusage() fallback from ext/standard/VmMemory::readRssBytes()
• VM RSS now uses /proc/self/statm only, matching lib/JIT/Builtin/MemoryRuntime.php JIT/AOT path
• Add test/unit/VmMemoryTest.php guarding against host delegation regression

Closes #7287

php-src reference

• ext/standard/basic_functions.c — memory_get_usage / zend_memory_usage
• PHP implementation: ext/standard/VmMemory.php + lib/JIT/Builtin/MemoryRuntime.php

Verification

./script/docker-exec.sh -- bash -lc 'source script/php-env.sh
vendor/bin/phpunit test/unit/VmMemoryTest.php
php bin/vm.php test/repro-maintainer/memory_native.php
php bin/vm.php -r "echo memory_get_usage(true), PHP_EOL;"
'

Output:

OK (2 tests, 4 assertions)
grow
peak
real
58073088

C runtime

No C changes — aligns VM with existing PHP LLVM MemoryRuntime (phpc_memory.c already deleted in #5377).

Follow-up

Top remaining C shrink candidate: lib/JIT/Builtin/hash_crypto_jit_runtime.c (~800 lines, #7189).

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