Take a borrow in invoke_exception instead of an owned type - #8327

• Closes Take &Py<PyType> instead of PyTypeRef in vm.invoke_exception() #8320
• This PR follows our AI policy

Summary

VirtualMachine::invoke_exception took its class argument as an owned PyTypeRef, but it never takes ownership — it only borrows cls for PyType::call (which itself is defined as fn call(zelf: &Py<Self>, ...)) and for Display in the error message. cls is never moved or stored.

Because the signature demanded ownership, callers holding only a borrow had to .to_owned() — an atomic refcount bump and later decrement — purely to satisfy the type, even though the reference was dropped immediately after the call. This changes the parameter to &Py<PyType>, the exact borrowed form (PyTypeRef = PyRef<PyType> derefs to Py<PyType>), and drops those .to_owned() calls.

Call sites updated:

ExceptionCtor::instantiate / instantiate_value own their cls via the self match, so they just pass &cls — no clone either way.

No behavior change; this is an API/ergonomics cleanup that removes unnecessary refcount churn and makes the helper consistent with the PyType::call it wraps.

Test plan

• test_exceptions, test_sys, test_io (667 tests, covering the BlockingIOError sites), extra_tests/snippets/builtin_exceptions.py: no regressions (the single test_exceptions failure, test_badisinstance, is pre-existing on main).
• Exercised each touched path manually: sys.exit / exit() / _thread.exit, raise ValueError and raise ValueError(...) via ExceptionCtor, ExceptionGroup, generator StopIteration, OSError from a failed open, and the genuine Err path of invoke_exception (a BaseException subclass whose __new__ returns a non-exception).
• cargo fmt --check / cargo clippy: clean.

Assisted-by: Claude Code:claude-fable-5

Summary by CodeRabbit

• Refactor
  • Streamlined internal exception creation across the runtime by avoiding unnecessary exception-type copies.
  • Preserved existing behavior for SystemExit, BlockingIOError, StopIteration, COM errors, and other exception paths.
  • Improved exception handling efficiency without changing public functionality or error messages.