Remove work-arounds for setting cell_contents #711

Job	Run time
Check types using pyright	46s
Build docs & run doctests	31s
Tests & Mypy on 3.7	59s
Verify dev env (ubuntu-latest)	15s
Tests & Mypy on 3.8	1m 16s
Tests & Mypy on 3.9	1m 1s
Verify dev env (windows-latest)	59s
Tests & Mypy on 3.10	1m 38s
Tests & Mypy on 3.11	2m 9s
Tests & Mypy on 3.12	1m 27s
Tests & Mypy on pypy-3.8	58s
Tests & Mypy on pypy-3.9	53s
Tests & Mypy on pypy-3.10	57s
Combine & check coverage.	12s
required-checks-pass	4s
	14m 5s

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