Fix CI format check: cargo fmt poly_python bridge

[liooil]

What

Fixes the failing Check formatting step in the RustPython bridge CI job (run #31169442915).

src/poly_python/src/lib.rs was not rustfmt-clean: 12 hunks (overlong match arms re-wrapped, trailing semicolons on block tail expressions). Formatting-only, no semantic changes.

Verification

cargo +nightly-2026-07-20 fmt --manifest-path src/poly_python/Cargo.toml -- --check  # passes

Same toolchain and config as CI (nightly-2026-07-20; rustfmt.toml only carries an ignore list, so defaults apply).