Share borrowed str and bytes checks - #9625

Summary

• Recognize b'*' as the all-elements wildcard in Element.iter, including bytes subclasses without calling an overridden equality method.
• Add ArgBytesOrStr for owned str/bytes arguments, with with_ref borrowing their byte payload and with_object_ref probing a borrowed object without allocation or Python conversion. Strings retain their raw WTF-8 representation; other buffer exporters are not accepted.
• Share the checks in ElementTree iteration, path detection, parser reads and event names, struct format matching, and bytes/bytearray hex separators. Event names no longer need a temporary byte vector. Original event objects and the hex separator's __len__ callback are preserved.

Validation

• cargo check --locked --offline -p rustpython-vm -p rustpython-stdlib --tests passed.
• cargo clippy --locked --offline -p rustpython-vm -p rustpython-stdlib --tests passed with the existing arc_with_non_send_sync warning at crates/vm/src/stdlib/_ctypes/base.rs:2246. A strict -D warnings run stops on that unchanged code.
• Two new Rust unit tests cover object identity, direct payload borrowing, owned lifetime, WTF-8, and rejection without calling the probe closure. They were compiled but not executed locally.
• Independent source review, normal commit hooks, and git diff --check passed.
• The original bytes wildcard behavior was compared with CPython 3.15.0. RustPython runtime tests and the full workspace/C-API suites were not run locally; hosted CI is still required.

AI assistance

Implementation and source review were assisted by OpenAI Codex.