Support --parallel option for CLI and Parallel option for test helper

[k1LoW]

No description provided.

[github-actions]

Code Metrics Report

	main (1a5cd62)	#211 (6db7738)	+/-
Coverage	78.9%	78.8%	-0.1%
Code to Test Ratio	1:0.8	1:0.8	-0.0

Details

  |                    | main (1a5cd62) | #211 (6db7738) |  +/-  |
  |--------------------|----------------|----------------|-------|
- | Coverage           |          78.9% |          78.8% | -0.1% |
  |   Files            |             27 |             27 |     0 |
  |   Lines            |           2750 |           2767 |   +17 |
+ |   Covered          |           2169 |           2180 |   +11 |
- | Code to Test Ratio |          1:0.8 |          1:0.8 |  -0.0 |
  |   Code             |           5379 |           5424 |   +45 |
+ |   Test             |           4232 |           4233 |    +1 |

Code coverage of files in pull request scope (76.2% → 76.4%)

Files	Coverage	+/-
book.go	63.6%	0.0%
operator.go	83.9%	+0.0%
option.go	46.5%	0.0%

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Reported by octocov