ci: run independent test checks in parallel

[kitsuyui]

Summary

• Run the independent lint, test, and build checks in .github/workflows/test.yml with GitHub Actions step-level parallel execution.
• Keep dist verification, schema verification, and build-size reporting sequential after the build completes.

Validation

• ruby -e 'require "yaml"; YAML.load_file(".github/workflows/test.yml"); puts "yaml ok"'
• biome check ./ via the pre-commit hook
• vitest run --coverage via the pre-push hook

Notes

• Local actionlint 1.7.12 does not recognize the new parallel step syntax yet and reports that the step is missing run or uses.

[github-actions]

🎉 Happy commit!

• dogfooding: PR ci: run independent test checks in parallel #851 always celebrates.
• dogfooding: f86f66ec0b61796c2b7f5b742d16942813e656ee always celebrates.

[github-actions]

Code Metrics Report

	main (3b12fd9)	#851 (49578eb)	+/-
Coverage	99.2%	99.2%	0.0%
Code to Test Ratio	1:1.3	1:1.3	0.0
Test Execution Time	1s	1s	0s

Details

  |                     | main (3b12fd9) | #851 (49578eb) | +/-  |
  |---------------------|----------------|----------------|------|
  | Coverage            |          99.2% |          99.2% | 0.0% |
  |   Files             |              5 |              5 |    0 |
  |   Lines             |            134 |            134 |    0 |
  |   Covered           |            133 |            133 |    0 |
  | Code to Test Ratio  |          1:1.3 |          1:1.3 |  0.0 |
  |   Code              |            714 |            714 |    0 |
  |   Test              |            966 |            966 |    0 |
  | Test Execution Time |             1s |             1s |   0s |

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Reported by octocov