Keep Rust checkout line endings compatible with rustfmt on Windows #867

Problem

PR #860 failed both Windows formatting jobs because core.autocrlf produced CRLF Rust sources while rustfmt.toml requires Unix newlines. This is one cause shared by amd64 and ARM64.

Reproduction

Failing run: https://github.com/wavefnd/Wave/actions/runs/37596302549 (jobs 112709682000 and 112709681443). Diagnostics: Incorrect newline style / FAIL Check formatting. At fb9243a, a core.autocrlf=true/core.eol=crlf checkout-index export produced CRLF in all 204 Rust files. With c50a7dd and *.rs text eol=lf, all 204 exported files use LF and cargo +1.89 fmt --all --check passes. Actual OS validation remains in PR CI.

Implementation status: Already implemented in open PR #860. This issue restores missing tracking; do not duplicate the implementation. Review and final PR validation remain with that PR.

Completion criteria

• Keep tracked Rust sources LF under Windows autocrlf checkout.
• Pass formatting on Windows amd64 and ARM64 without skipping the gate.
• Preserve unrelated platform and fixture line-ending policies.