chore: remove pyrfc3339 and change to datetime.datetime.fromisoformat… #1344

Job	Run time
Build test (3.10)	20s
Unit tests (3.8)	30s
Unit tests (3.9)	27s
Validate (3.10)	24s
Unit tests (3.10)	30s
Unit tests (3.11)	21s
Unit tests (3.12)	24s
Unit tests (3.13)	37s
Quarantined Integration Tests (3.10, 3.1/stable)	40m 57s
Integration (3.10, 3.1/stable, True)	37m 2s
Quarantined Integration Tests (3.10, 3.3/stable)	40m 41s
Integration (3.10, 3.1/stable, False)	39m 21s
Quarantined Integration Tests (3.10, 3.4/stable)	52m 6s
Integration (3.10, 3.3/stable, True)	42m 16s
Quarantined Integration Tests (3.10, 3.5/stable)	47m 39s
Integration (3.10, 3.3/stable, False)	38m 8s
Quarantined Integration Tests (3.10, 3.6/stable)	48m 24s
Integration (3.10, 3.4/stable, True)	37m 53s
Integration (3.10, 3.4/stable, False)	38m 17s
Integration (3.10, 3.5/stable, True)	42m 34s
Integration (3.10, 3.5/stable, False)	37m 40s
Integration (3.10, 3.6/stable, True)	37m 53s
Integration (3.10, 3.6/stable, False)	39m 8s
	10h 23m 32s

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