fix: safeAlloc infinite recursion — called itself instead of exports.alloc

safeAlloc() was calling this.safeAlloc(bytes) instead of
this.exports.alloc(bytes), causing infinite recursion and stack
overflow on every WASM operation. This broke all 57 call sites:
decompression, column registration, fragment building, vector search,
IVF-PQ index loading, and every WASM memory allocation path.

Not caught by tests because node tests mock WASM and workerd tests
use a separate config.

Author: teamchong

src/wasm-engine.ts

@@ -174,7 +174,7 @@ export class WasmEngine {
   /** Alloc with i32 overflow guard — returns 0 if byte size exceeds WASM i32 range. */
   private safeAlloc(bytes: number): number {
     if (bytes > 0x7FFF_FFFF) return 0;
-    return this.safeAlloc(bytes);
+    return this.exports.alloc(bytes);
   }
 
   reset(): void { this.exports.resetResult(); }