simplify expression of cooling terms in x-lumped thermal models #7774

Job	Run time
style	23s
Doctests (ubuntu-latest / Python 3.11)	6m 14s
Example notebooks (ubuntu-latest / Python 3.11)	25m 8s
Coverage tests (ubuntu-latest / Python 3.11)	28m 49s
Integration tests (ubuntu-latest / Python 3.8)	16m 35s
Example scripts (ubuntu-latest / Python 3.11)	14m 59s
Integration tests (ubuntu-latest / Python 3.9)	18m 50s
Unit tests (ubuntu-latest / Python 3.8)	14m 33s
Integration tests (ubuntu-latest / Python 3.10)	17m 34s
Unit tests (ubuntu-latest / Python 3.9)	14m 21s
Integration tests (ubuntu-latest / Python 3.11)	15m 8s
Unit tests (ubuntu-latest / Python 3.10)	16m 26s
Integration tests (macos-latest / Python 3.8)	22m 23s
Unit tests (macos-latest / Python 3.8)	17m 37s
Integration tests (macos-latest / Python 3.9)	22m 6s
Unit tests (macos-latest / Python 3.9)	12m 31s
Integration tests (macos-latest / Python 3.10)	22m 29s
Unit tests (macos-latest / Python 3.10)	19m 36s
Integration tests (macos-latest / Python 3.11)	25m 24s
Unit tests (macos-latest / Python 3.11)	22m 26s
Integration tests (windows-latest / Python 3.8)	15m 32s
Unit tests (windows-latest / Python 3.8)	13m 27s
Integration tests (windows-latest / Python 3.9)	16m 28s
Unit tests (windows-latest / Python 3.9)	11m 48s
Integration tests (windows-latest / Python 3.10)	20m 4s
Unit tests (windows-latest / Python 3.10)	11m 49s
Integration tests (windows-latest / Python 3.11)	16m 16s
Unit tests (windows-latest / Python 3.11)	12m 24s
	7h 51m 20s

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