Format workflow: auto-fix and commit formatting/lint issues; extend coverage to tests/**/*.rs

[Copilot]

The format workflow only reported issues without fixing them, and skipped all .rs files under tests/ that aren't part of a Cargo project.

Workflow changes

• permissions: contents: write + checkout with ref: ${{ github.head_ref || github.ref_name }} so the action can push back to the correct branch
• Auto-fix phase (runs before the existing check steps):
  • clang-format -i for C++
  • cargo clippy --fix --allow-dirty for all three Rust crates (runs before cargo fmt so clippy's edits are normalized by rustfmt)
  • cargo fmt for all three Rust crates
  • rustfmt across tests/**/*.rs
• stefanzweifel/git-auto-commit-action@v5 commits any resulting changes back to the branch automatically
• Existing check steps remain unchanged as a verification pass (catches anything that can't be auto-fixed)

Coverage gap: tests/**/*.rs

These files are lit-test expected outputs compared byte-for-byte against cpp2rust output. They can't be linted by clippy without a Cargo project context, but rustfmt runs on them directly. Since cpp2rust already calls rustfmt on its output, keeping the expected files formatted with the same pinned toolchain (1.94.0) keeps them consistent.

Auto-fixes applied in this PR

Running the new workflow locally produced these fixes (now committed):

• rules/build.rs: collapsible_if and collapsible_str_replace clippy suggestions
• tests/unit/out/refcount/ub*.rs (22 files): import order normalized to rustfmt 1.94.0
• tests/unit/out/unsafe/bit_cast.rs: redundant braces removed (use libcc2rs::{prepostfix::*} → use libcc2rs::prepostfix::*)