Add IArray::get_mut and IArray::make_mut (#36) #69

Job	Run time
test (ubuntu-latest, stable, 1.9.3)	15s
test (ubuntu-latest, stable, latest)	15s
test (ubuntu-latest, 1.64.0, 1.9.3)	4m 30s
test (ubuntu-latest, 1.64.0, latest)	5m 18s
test (windows-latest, stable, 1.9.3)	1m 43s
test (windows-latest, stable, latest)	1m 48s
test (windows-latest, 1.64.0, 1.9.3)	6m 35s
test (windows-latest, 1.64.0, latest)	6m 52s
test (macos-latest, stable, 1.9.3)	20s
test (macos-latest, stable, latest)	53s
test (macos-latest, 1.64.0, 1.9.3)	4m 58s
test (macos-latest, 1.64.0, latest)	5m 9s
	38m 36s

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