Draft changes to BaseModel for multi-fitting #1715

Job	Run time
style	16s
Coverage tests (macos-14 / Python 3.12)	1m 32s
Integration tests (ubuntu-latest / Python 3.12)	6m 13s
Unit tests (ubuntu-latest / Python 3.9)	1m 17s
Integration tests (windows-latest / Python 3.12)	9m 43s
Test examples (ubuntu-latest / Python 3.12)	12m 29s
Unit tests (ubuntu-latest / Python 3.10)	1m 16s
Integration tests (macos-13 / Python 3.12)	6m 5s
Test examples (windows-latest / Python 3.12)	11m 26s
Unit tests (ubuntu-latest / Python 3.11)	1m 15s
Test examples (macos-13 / Python 3.12)	14m 3s
Integration tests (macos-14 / Python 3.12)	2m 49s
Unit tests (ubuntu-latest / Python 3.12)	1m 12s
Test examples (macos-14 / Python 3.12)	5m 35s
Unit tests (windows-latest / Python 3.9)	2m 12s
Unit tests (windows-latest / Python 3.10)	3m 8s
Unit tests (windows-latest / Python 3.11)	3m 31s
Unit tests (windows-latest / Python 3.12)	3m 35s
Unit tests (macos-13 / Python 3.9)	1m 12s
Unit tests (macos-13 / Python 3.10)	1m 50s
Unit tests (macos-13 / Python 3.11)	1m 24s
Unit tests (macos-13 / Python 3.12)	1m 20s
Unit tests (macos-14 / Python 3.9)	57s
Unit tests (macos-14 / Python 3.10)	1m 27s
Unit tests (macos-14 / Python 3.11)	1m 4s
	1h 36m 51s

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