chore: clean up oxlint pedantic warnings

[YogliB]

Summary

What

Cleaned up the current oxlint pedantic warnings by refactoring test helpers and splitting an oversized unit test file.

Why

Keep the lint bar higher without silencing rules or weakening the current quality gate.

Changes

• Simplified mock helpers in test/helpers.ts to remove unnecessary async/promise wrappers while keeping the same call shapes for callers.
• Kept the integration runner contract intact in test/integration/runner.ts while removing a redundant async wrapper.
• Removed unnecessary async wrappers from the lazy git test mocks in test/unit/lazy-git.test.ts.
• Split the long redirect-fetch coverage in test/unit/utils.test.ts into smaller describe blocks so the file passes pedantic without disabling max-lines-per-function.
• Left pedantic enabled at warn in .oxlintrc.json so future warnings stay visible.

Testing

How you verified this (commands, scenarios, or N/A):

• bunx oxlint --import-plugin --deny-warnings test/helpers.ts test/integration/runner.ts test/unit/lazy-git.test.ts test/unit/utils.test.ts

• bun run test was not run; the verification here was the focused lint pass plus targeted unit/integration tests.

• Targeted tests passed: 11/11.

• Automated tests (bun run test)

• Manual / CLI check if user-facing behavior changed

• CI passes

Review notes

Breaking changes (or none)

None.

Risks / rollout (or none)

Low risk; the change is test-only cleanup with no production code behavior changes.

Focus areas for reviewers (optional)

The main thing to verify is that the helper refactors preserve the existing async/mock contract and that no lint rule was suppressed.

Checklist

• Error paths and exit codes considered where relevant
• Help text, completions, or docs updated if user-facing strings changed
• Squashed to a single commit
• No unrelated drive-by changes