Add nanosecond precision to `File.utime` on Unix #13189

Job	Run time
check_format	1m 37s
x86_64-gnu-test (1.7.3)	36m 23s
x86_64-gnu-test (1.8.2)	34m 52s
x86_64-gnu-test-preview_mt	5m 48s
x86_64-musl-test	36m 58s
x86_64-gnu-test (1.9.2)	35m 48s
x86_64-gnu-test (1.10.1)	32m 52s
x86_64-gnu-test (1.11.2)	35m 6s
x86_64-gnu-test (1.12.2)	34m 44s
x86_64-gnu-test (1.13.3)	34m 56s
x86_64-gnu-test (1.14.0)	34m 5s
x86_64-gnu-test (1.0.0, FLAGS=-Dwithout_ffi USE_PCRE1=true)	32m 24s
x86_64-gnu-test (1.1.1, FLAGS=-Dwithout_ffi USE_PCRE1=true)	33m 0s
x86_64-gnu-test (1.2.2, USE_PCRE1=true)	33m 33s
x86_64-gnu-test (1.3.2, USE_PCRE1=true)	32m 7s
x86_64-gnu-test (1.4.1, USE_PCRE1=true)	33m 28s
x86_64-gnu-test (1.5.1, USE_PCRE1=true)	33m 56s
x86_64-gnu-test (1.6.2, USE_PCRE1=true)	31m 53s
	9h 13m 30s

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