Run test files concurrently

[holyfuchs]

Test files now run in parallel.

On an M4 Mac, 20 files × 100 transactions improved from 88s → 25s. (about 3.5× faster)

Each test file runs in its own isolated runner. The new --jobs flag caps concurrency (default: number of CPU cores).

Also in this PR:

• Fix data races in lint_test.go and test_test.go caused by shared Flowkit global state
• Fix a race in settings.loadViper using sync.Once

These fixes were required to validate the concurrent test runner under -race.

Some remaining races originate from upstream dependencies and are unrelated to this PR. They will be addressed in follow-up PRs:

• Make Greetings generator counter thread-safe flow-go-sdk#1009
• Fix spinner race condition flowkit#202
• fix: eliminate data races in Debugger and ServiceKey flow-emulator#977

Note: Refactoring testCode into smaller helpers is planned, but will be done in a separate PR to make this review easier.

[github-actions]

Dependency Review

✅ No vulnerabilities or license issues or OpenSSF Scorecard issues found.

Scanned Files

None

[codecov-commenter]

Codecov Report

❌ Patch coverage is 93.06931% with 7 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
internal/test/test.go	93.06%	5 Missing and 2 partials ⚠️

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