Route Linux Rust CI to Incredibuild runners

[zozo123]

Summary

• Route the Linux Rust-heavy CI jobs to incredibuild-runner using only runner selector changes.
• Keep all commands, env, cache config, and scripts unchanged so this exercises the runner image's out-of-the-box cargo shim.
• Leave CodSpeed on ubuntu-latest; its full run path needs Valgrind/setarch and has a separate auth/upload issue in current CI.

Diff snippet

-    runs-on: ubuntu-latest
+    runs-on: incredibuild-runner

Applied to:

• test-rust
• test-python-coverage
• bench-test
• miri
• build-js Linux x86_64-unknown-linux-gnu
• build-js wasm32-wasip1-threads

Evidence

• Evidence PR with probes and benchmarks: ci: route heavy Rust jobs through Incredibuild build runners #1
• vnext cargo shim for normal cargo commands: https://github.com/Incredibuild-RND/vnext-processing-engine/pull/210
• vnext cargo shim for llvm-cov, codspeed build, and miri test: https://github.com/Incredibuild-RND/vnext-processing-engine/pull/215
• Live runner shim probe: https://github.com/Incredibuild-RND/monty/actions/runs/25792436510
• Latest evidence CI: https://github.com/Incredibuild-RND/monty/actions/runs/25793334544
• Latest evidence benchmark: https://github.com/Incredibuild-RND/monty/actions/runs/25793332007

Evidence numbers

• Real test-rust: 346.8s on ubuntu-latest -> 267.6s on IB (1.30x) in the latest cap-safe validation.
• Synthetic warm cache: 38.6s -> 18.9s (2.05x) in the latest validation.
• Historical identical-workload warm-cache ceiling from the evidence branch: about 7x-8.7x.

Test plan

• GitHub Actions on this PR.
• This PR intentionally does not carry the evidence branch's helper scripts or benchmark workflows.

Made with Cursor

[zozo123]

Validation update for the strict runs-on-only PR:

• This PR still contains only .github/workflows/ci.yml runner selector changes: 1 file, 6 selector replacements.
• First CI run proved the runner image path is partially ready: test-python-coverage and miri passed on incredibuild-runner.
• test-rust and bench-test failed at link time with rust-lld: error: unable to find library -lpython3.14.

Root cause: the current runner image exports a shared CARGO_TARGET_DIR=/ib-workspace/cache/cargo-target. Cargo target dirs contain absolute build-script metadata; pyo3 reused metadata pointing at a different setup-python toolcache path. That is an out-of-box runner image issue, not a Monty workflow issue.

Upstream fix opened here: https://github.com/Incredibuild-RND/vnext-processing-engine/pull/216

After that is merged and the runner image is rebuilt/deployed, rerun this PR's CI without changing this PR.