fix(lsp/php): prevent OOM when a PHP trait uses itself

[muba00]

What does this PR do?

Fixes an unbounded memory blow-up (observed 40 GB+, freezing the host)
when the PHP Hybrid-LSP pass indexes a file whose trait uses itself. It was
hit in a real project by a 4-line trait; the only workaround was to add the file
to .cbmignore.

Minimal reproducer (index_repository, mode: "full" — runs away on main):

<?php
namespace App;
trait EnumTrait {
    use EnumTrait;                                  // trait adopts itself
    public function getRandom(): int { return 1; }
}

It also triggers via an alias that resolves back to the enclosing trait by short
name, which is how it appeared in the wild (use Vendor\EnumTrait as X; use X;
inside a trait that is itself named EnumTrait).

Root cause

flatten_trait_into_class() in internal/cbm/lsp/php_lsp.c copies a trait's
methods onto the using class by iterating the type registry with a live upper
bound:

for (int i = 0; i < reg->func_count; i++) {         // bound grows inside the loop
    if (strcmp(src->receiver_type, canonical_trait_qn) != 0) continue;
    ...
    rf.receiver_type = class_qn;                     // copy tagged with the user
    cbm_registry_add_func(reg, rf);                  // APPENDS → func_count++
}

cbm_registry_add_func() appends to the very array being iterated (no dedup) and
increments reg->func_count. Normally the copies get receiver_type = class_qn,
which differs from the trait, so they don't re-match and the loop ends.

When a trait adopts itself, class_qn == canonical_trait_qn, so every copied
method is tagged with the trait's own QN and re-matches the loop filter —
appending another method and pushing the bound out ahead of i. The loop never
terminates, arena-allocating a fresh method each pass until memory is exhausted.

(Confirmed by differential reduction — self-adoption + ≥1 member + a trait use
are each necessary — and a live sample(1) showing flatten_trait_into_class → cbm_arena_sprintf with the footprint climbing through 6 GB.)

Fix (internal/cbm/lsp/php_lsp.c)

1. Short-circuit self-flattening — a trait cannot meaningfully use itself
   (PHP raises "Trait X cannot use itself"), so return early when
   class_qn == canonical_trait_qn. This removes the only path by which an
   appended func can re-match the filter.
2. Snapshot the loop bound before iterating, so entries appended during the
   loop are never revisited — closing the mutate-while-iterating hazard
   structurally, independent of (1).

Checklist

• Every commit is signed off (git commit -s) — DCO trailer present
• Tests pass locally — full build/c/test-runner (ASan+UBSan): 5916 passed,
  1 skipped, 0 failures, 0 sanitizer errors; php_lsp suite 279/279
• Lint passes (make -f Makefile.cbm lint-ci) — could not run locally
  (clang-format / clang-tidy / cppcheck not installed). Diff manually checked
  against .clang-format (LLVM, ColumnLimit 100: added lines ≤ 79, 4-space
  indent, attach braces) and mirrors the surrounding formatted code; please
  let CI verify.
• New behavior is covered by a test (reproduce-first) — added
  phplsp_trait_self_use_terminates, confirmed it hangs/OOMs on pre-fix
  code and passes after the fix.

---

Verified end to end: the production binary now indexes the original triggering
file (and its real-world siblings) in < 0.5 s at ~6 MB RSS instead of running
away.