chore: separate out func handleBlockquote

[Songmu]

SSIA

[github-actions]

Code Metrics Report

	main (f20e82f)	#418 (54374a4)	+/-
Coverage	32.3%	32.3%	+0.0%
Code to Test Ratio	1:0.8	1:0.8	-0.1
Test Execution Time	11s	10s	-1s

Details

  |                     | main (f20e82f) | #418 (54374a4) |  +/-  |
  |---------------------|----------------|----------------|-------|
+ | Coverage            |          32.3% |          32.3% | +0.0% |
  |   Files             |             27 |             28 |    +1 |
  |   Lines             |           3121 |           3120 |    -1 |
  |   Covered           |           1010 |           1010 |     0 |
- | Code to Test Ratio  |          1:0.8 |          1:0.8 |  -0.1 |
  |   Code              |           6422 |           6432 |   +10 |
  |   Test              |           5630 |           5630 |     0 |
+ | Test Execution Time |            11s |            10s |   -1s |

Code coverage of files in pull request scope (1.3% → 1.3%)

Files	Coverage	+/-	Status
apply.go	1.4%	+0.0%	modified
blockquote.go	0.0%	0.0%	added

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Reported by octocov