fix: release PyObject.call result references after GC

[mchao123]

Summary

PyObject.call() receives a new Python reference from PyObject_Call, but the returned PyObject is not registered with the module's FinalizationRegistry. Once the JS wrapper is collected, that native reference is never released.

This is observable without memory profiling:

100 calls to a function returning the same object
Python refcount: 3 -> 103

The added regression test asserts that the refcount returns to its baseline after GC.

Fix

Register the call result with refregistry, tying the new Python reference to the lifetime of its JS wrapper. Existing .owned semantics remain unchanged.

Verification

• deno task test
  • test/test.ts: 15 passed
  • test/test_with_gc.ts: 4 passed
• deno task check
• deno fmt --check

[DjDeveloperr]

LGTM, thank you!