feat: stabilize Cell class

[lars-reimann]

Closes partially #977

Summary of Changes

• Add method Cell.constant to create a cell with a constant value from a Python literal
• Add method Cell.date to create a cell with a date
• Add method Cell.time to create a cell with a time
• Add method Cell.datetime to create a cell with a datetime
• Add method Cell.duration to create a cell with a duration
• Add method Cell.cast to cast a cell to another type
• Improve type hints for cell operations

[github-actions]

🦙 MegaLinter status: ✅ SUCCESS

Descriptor	Linter	Files	Fixed	Errors	Elapsed time
✅ PYTHON	black	60	0	0	1.63s
✅ PYTHON	mypy	60		0	3.63s
✅ PYTHON	ruff	60	0	0	0.29s
✅ REPOSITORY	git_diff	yes		no	0.28s

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[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 95.16%. Comparing base (dc4640b) to head (a70c635).
Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #984      +/-   ##
==========================================
+ Coverage   95.09%   95.16%   +0.07%     
==========================================
  Files         125      127       +2     
  Lines        7719     7790      +71     
==========================================
+ Hits         7340     7413      +73     
+ Misses        379      377       -2     

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