IString: implement From<std::fmt::Arguments> for IString #132

Job	Run time
test (ubuntu-latest, stable, 1.9.3)	36s
test (ubuntu-latest, stable, latest)	40s
test (ubuntu-latest, 1.64.0, 1.9.3)	2m 53s
test (ubuntu-latest, 1.64.0, latest)	2m 52s
test (windows-latest, stable, 1.9.3)	1m 34s
test (windows-latest, stable, latest)	1m 50s
test (windows-latest, 1.64.0, 1.9.3)	3m 42s
test (windows-latest, 1.64.0, latest)	3m 49s
test (macos-latest, stable, 1.9.3)	1m 36s
test (macos-latest, stable, latest)	1m 5s
test (macos-latest, 1.64.0, 1.9.3)	5m 20s
test (macos-latest, 1.64.0, latest)	7m 20s
	33m 17s

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