test(memory): add deterministic OOM fault-injection coverage

[TrixNEW]

Problem

Fuzzing and soak tests do not guarantee every allocation-failure path is tested.

zphp uses manual ownership, reference counting, pools, GC, and native resources, so an OOM at the wrong point can cause leaks or partially corrupted runtime state.

Changes

Use Zig's failing allocator testing to intentionally fail the Nth allocation and verify cleanup.

Prioritize:

• PhpArray.append/set
• objects/properties
• strings
• references
• closures
• cycle collection
• exceptions
• native resources
• VM reset/deinit
• zphp serve worker startup

Verify after each failure

• no leaked allocations/refcounts
• no double-free or use-after-free
• no partially modified arrays
• no stale GC/tracking entries
• no leaked sockets/file descriptors/native resources

Acceptance criteria

• Core ownership-sensitive operations have deterministic OOM tests.
• Failed allocations leave the runtime valid or cleanly terminated.
• The fault-injection suite runs in CI.