refactor(uptime): use FluentArgs for loadavg formatting in get_format #16620

Job	Run time
Build and test uufuzz examples	1m 6s
Build the fuzzers	2m 50s
Fuzz (fuzz_expr, true)	2m 12s
Fuzz (fuzz_sort, false)	1m 25s
Fuzz (fuzz_test, true)	2m 7s
Fuzz (fuzz_cksum, false)	1m 4s
Fuzz (fuzz_cut, false)	1m 7s
Fuzz (fuzz_echo, true)	2m 3s
Fuzz (fuzz_non_utf8_paths, true)	2m 8s
Fuzz (fuzz_tr, false)	1m 34s
Fuzz (fuzz_parse_glob, true)	2m 4s
Fuzz (fuzz_printf, true)	2m 14s
Fuzz (fuzz_split, false)	1m 32s
Fuzz (fuzz_date, true)	2m 16s
Fuzz (fuzz_env, false)	1m 5s
Fuzz (fuzz_parse_time, true)	1m 44s
Fuzz (fuzz_wc, false)	1m 4s
Fuzz (fuzz_parse_size, true)	1m 3s
Fuzz (fuzz_seq_parse_number, true)	1m 9s
Fuzz (fuzz_seq, false)	1m 10s
Fuzzing Summary	11s
	33m 8s

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