fix(ci): unset CARGO_INCREMENTAL in workflows

[hanabi1224]

Summary of changes

The unit test workflow compiles the project several times (nextest -> cargo test -> cargo test --doc ) and should benefit from the incremental build.

https://doc.rust-lang.org/cargo/reference/profiles.html?highlight=incremental#incremental

Incremental compilation causes rustc to save additional information to disk which will be reused when recompiling the crate, improving re-compile times. The additional information is stored in the target directory.

Changes introduced in this pull request:

• unset CARGO_INCREMENTAL to enable incremental build

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
  • Simplified CI workflows by removing explicit overrides so the build system uses default incremental behavior.
  • Increased unit-test concurrency to speed CI feedback (build jobs raised from 2 to 3).
• Performance
  • Enabled incremental compilation and increased parallel code generation for the quick build profile to improve build times.

[coderabbitai]

Walkthrough

Removed explicit CARGO_INCREMENTAL: 0 from multiple GitHub Actions workflows and added a quick cargo profile with incremental = true and codegen-units = 256 in Cargo.toml. Also increased CARGO_BUILD_JOBS from 2 to 3 in the unit-tests workflow.

Changes

Cohort / File(s)	Summary
Workflows — removed forced incremental env .github/workflows/butterflynet.yml, .github/workflows/coverage.yml, .github/workflows/docker.yml, .github/workflows/forest.yml, .github/workflows/rust-lint.yml, .github/workflows/unit-tests.yml	Removed CARGO_INCREMENTAL: 0 from workflow env sections; unit-tests workflow also increased CARGO_BUILD_JOBS from 2 to 3.
Cargo profile Cargo.toml	Added [profile.quick] settings: incremental = true and codegen-units = 256 (enables incremental compilation and increases codegen parallelism).

Estimated code review effort

🎯 3 (Moderate) | ⏱️ ~20 minutes

Possibly related PRs

• fix(ci): speed up CI builds with quick profile #6504: Adds/configures a "quick" cargo profile and removes forced CARGO_INCREMENTAL in CI — closely related to the cargo profile and workflow env removals.
• fix(ci): set CARGO_BUILD_JOBS=2 for unit tests #6538: Modifies CARGO_BUILD_JOBS in .github/workflows/unit-tests.yml — overlaps with the unit-tests concurrency change.

Suggested reviewers

• LesnyRumcajs
• akaladarshi

🚥 Pre-merge checks | ✅ 3

✅ Passed checks (3 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly describes the main change: unsetting CARGO_INCREMENTAL in CI workflows. It directly summarizes the primary modification across all affected workflow files.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.

_{✏️ Tip: You can configure your own custom pre-merge checks in the settings.}

✨ Finishing touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Post copyable unit tests in a comment
• Commit unit tests in branch hm/ci-ut-incremental-build

---

_{Comment @coderabbitai help to get the list of available commands and usage tips.}

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 63.33%. Comparing base (a25c85a) to head (67ee89a).
⚠️ Report is 3 commits behind head on main.

Additional details and impacted files

see 2 files with indirect coverage changes

---

Continue to review full report in Codecov by Sentry.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update a25c85a...67ee89a. Read the comment docs.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.

[LesnyRumcajs]

Let's elaborate here how this helps.

[hanabi1224]

Let's elaborate here how this helps.

@LesnyRumcajs updated in the description.