Parallelize independent workflow checks

[kitsuyui]

Summary

• Run independent lint, type-check, test, and build steps through GitHub Actions parallel groups.
• Keep packaging, safe-directory setup, build-size measurement, and coverage reporting after the parallel group.

Verification

• Parsed the updated workflows as YAML.
• bun run lint
• bun run typecheck
• bun run build
• bun pm pack
• bun run test requires Docker locally; CI provides a container and httpbin service for this job.

[github-actions]

Code Metrics Report

	main (de5f702)	#1648 (143732d)	+/-
Coverage	86.9%	86.9%	0.0%
Code to Test Ratio	1:0.5	1:0.5	0.0
Test Execution Time	6s	7s	+1s

Details

  |                     | main (de5f702) | #1648 (143732d) | +/-  |
  |---------------------|----------------|-----------------|------|
  | Coverage            |          86.9% |           86.9% | 0.0% |
  |   Files             |             11 |              11 |    0 |
  |   Lines             |            207 |             207 |    0 |
  |   Covered           |            180 |             180 |    0 |
  | Code to Test Ratio  |          1:0.5 |           1:0.5 |  0.0 |
  |   Code              |           1648 |            1648 |    0 |
  |   Test              |            961 |             961 |    0 |
- | Test Execution Time |             6s |              7s |  +1s |

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Reported by octocov