Improve method source toggling #924

Job	Run time
lint	13s
ruby-versions / Generate Ruby versions	3s
test (3.0, ubuntu-latest)	22s
test (3.0, macos-latest)	21s
test (3.0, windows-latest)	1m 39s
test (3.1, ubuntu-latest)	24s
test (3.1, macos-latest)	22s
test (3.1, windows-latest)	1m 22s
test (3.2, ubuntu-latest)	25s
test (3.2, macos-latest)	20s
test (3.2, windows-latest)	1m 50s
test (3.3, ubuntu-latest)	23s
test (3.3, macos-latest)	33s
test (3.3, windows-latest)	1m 37s
test (head, ubuntu-latest)	33s
test (head, macos-latest)	21s
test (head, windows-latest)	1m 28s
test (jruby, ubuntu-latest)	1m 58s
test (jruby, macos-latest)	1m 15s
test (jruby-head, ubuntu-latest)	1m 54s
test (jruby-head, macos-latest)	1m 15s
test (truffleruby, ubuntu-latest)	2m 18s
test (truffleruby, macos-latest)	1m 43s
test (truffleruby-head, ubuntu-latest)	3m 24s
test (truffleruby-head, macos-latest)	2m 7s
	28m 10s

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