chore(ci): speed up linking with mold

[hanabi1224]

Summary of changes

main: https://github.com/ChainSafe/forest/actions/runs/26050369083/job/76585211911#step:11:1649

    Finished `codecov` profile [optimized + debuginfo] target(s) in 4m 22s
     Running `target/llvm-cov-target/codecov/forest-dev fetch-test-snapshots --actor-bundle /var/tmp/forest_actor_bundle.car.zst`

   Compiling forest-filecoin v0.33.4 (/runner/_work/forest/forest)
    Finished `codecov` profile [optimized + debuginfo] target(s) in 3m 31s
     Running unittests src/lib.rs (target/llvm-cov-target/codecov/deps/forest-387a6e99d9f41bf2)

pr: https://github.com/ChainSafe/forest/actions/runs/26073171333/job/76658639121?pr=7078#step:12:1649

    Finished `codecov` profile [optimized + debuginfo] target(s) in 3m 54s
     Running `target/llvm-cov-target/codecov/forest-dev fetch-test-snapshots --actor-bundle /var/tmp/forest_actor_bundle.car.zst`

   Compiling forest-filecoin v0.33.4 (/runner/_work/forest/forest)
    Finished `codecov` profile [optimized + debuginfo] target(s) in 3m 09s
     Running unittests src/lib.rs (target/llvm-cov-target/codecov/deps/forest-b726eb5360158a63)

Changes introduced in this pull request:

Reference issue to close (if applicable)

Closes

Other information and links

Change checklist

• I have performed a self-review of my own code,
• I have made corresponding changes to the documentation. All new code adheres to the team's documentation standards,
• I have added tests that prove my fix is effective or that my feature works (if possible),
• I have made sure the CHANGELOG is up-to-date. All user-facing changes should be reflected in this document.

Outside contributions

• I have read and agree to the CONTRIBUTING document.
• I have read and agree to the AI Policy document. I understand that failure to comply with the guidelines will lead to rejection of the pull request.

Summary by CodeRabbit

• Chores
  • Updated CI workflows to use a new Rust linker configuration across build, coverage, Docker, and integration jobs—aimed at faster and more reliable CI builds and artifacts.

[coderabbitai]

Walkthrough

Four GitHub Actions workflows add rui314/setup-mold@v1 and update RUSTFLAGS to use -fuse-ld=mold instead of -fuse-ld=lld so all CI Rust builds link with the mold linker.

Changes

Linker configuration migration to mold

Layer / File(s)	Summary
Mold linker setup across workflows .github/workflows/butterflynet.yml, .github/workflows/coverage.yml, .github/workflows/docker.yml, .github/workflows/forest.yml	Each workflow inserts rui314/setup-mold@v1 (configured with make-default: false) before build steps to install/configure the mold linker.
RUSTFLAGS updates to use mold for linking .github/workflows/butterflynet.yml, .github/workflows/coverage.yml, .github/workflows/docker.yml, .github/workflows/forest.yml	Each workflow updates its RUSTFLAGS to pass -fuse-ld=mold (or -C link-arg=-fuse-ld=mold) replacing prior -fuse-ld=lld.

Estimated code review effort

🎯 2 (Simple) | ⏱️ ~10 minutes

Possibly related PRs

• ChainSafe/forest#6340: Modifies .github/workflows/coverage.yml with linker/RUSTFLAGS changes for Codecov builds.

Suggested labels

github_actions

Suggested reviewers

• LesnyRumcajs
• sudo-shashank

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Title check	✅ Passed	The pull request title accurately reflects the main change: updating CI workflows to use the mold linker for faster linking.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.

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✨ Finishing Touches

📝 Generate docstrings

• Create stacked PR
• Commit on current branch

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch hm/speed-up-linking-with-mold

✨ Simplify code

• Create PR with simplified code
• Commit simplified code in branch hm/speed-up-linking-with-mold

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