feat: use flymake-popon instead of sideline-flymake #1530

Job	Run time
test (ubuntu-latest, 27.2, false)	1m 6s
test (ubuntu-latest, 28.2, false)	1m 52s
test (ubuntu-latest, 29.4, false)	4m 10s
test (macos-latest, 27.2, false)	1m 9s
test (macos-latest, 28.2, false)	1m 53s
test (macos-latest, 29.4, false)	4m 22s
test (windows-latest, 27.2, false)	1m 9s
test (windows-latest, 28.2, false)	1m 41s
test (windows-latest, 29.4, false)	4m 1s
test (ubuntu-latest, snapshot, true)	3m 18s
test (macos-latest, snapshot, true)	2m 50s
test (windows-latest, snapshot, true)	3m 16s
	30m 47s

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