Improve method source toggling #931

Job	Run time
lint	14s
ruby-versions / Generate Ruby versions	3s
test (3.0, ubuntu-latest)	23s
test (3.0, macos-latest)	24s
test (3.0, windows-latest)	1m 46s
test (3.1, ubuntu-latest)	28s
test (3.1, macos-latest)	22s
test (3.1, windows-latest)	1m 57s
test (3.2, ubuntu-latest)	27s
test (3.2, macos-latest)	28s
test (3.2, windows-latest)	1m 37s
test (3.3, ubuntu-latest)	22s
test (3.3, macos-latest)	20s
test (3.3, windows-latest)	2m 45s
test (head, ubuntu-latest)	44s
test (head, macos-latest)	24s
test (head, windows-latest)	1m 17s
test (jruby, ubuntu-latest)	1m 58s
test (jruby, macos-latest)	1m 21s
test (jruby-head, ubuntu-latest)	2m 4s
test (jruby-head, macos-latest)	1m 15s
test (truffleruby, ubuntu-latest)	2m 26s
test (truffleruby, macos-latest)	2m 10s
test (truffleruby-head, ubuntu-latest)	3m 11s
test (truffleruby-head, macos-latest)	2m 13s
	30m 39s

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