Refactor `pint.fitter` #4827

Job	Run time
macos-latest-py313	1h 7m 0s
ubuntu-latest, ephemeris_connection	1m 14s
ubuntu-latest, black	22s
ubuntu-latest, py313-test-cov	1h 34m 6s
ubuntu-latest, notebooks	5m 32s
ubuntu-latest, oldestdeps	30m 13s
	3h 18m 27s

Provide feedback