feat: make Column and Row iterable

[lars-reimann]

Closes #47.

Summary of Changes

• Add __iter__ method to Column and Row to iterate over the values:
  • Iterating over a Column returns the values.
  • Iterating over a Row returns the column names, as specified in the documenetation of __iter__.
• Add __len__ method to Column and Row to compute their length.
• Change superclasses of exceptions as needed for __getitem__:
  • Change superclass of IndexOutOfBoundsError to IndexError.
  • Change superclass of UnknownColumnNameError to KeyError.

[lars-reimann]

🦙 MegaLinter status: ✅ SUCCESS

Descriptor	Linter	Files	Fixed	Errors	Elapsed time
✅ PYTHON	black	14	0	0	0.68s
✅ PYTHON	flake8	14		0	0.41s
✅ PYTHON	isort	14	0	0	0.27s
✅ PYTHON	mypy	14		0	1.8s
✅ PYTHON	pylint	14		0	2.15s
✅ REPOSITORY	git_diff	yes		no	0.03s

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[codecov]

Codecov Report

Merging #55 (1922f60) into main (c3fd3b5) will increase coverage by 0.07%.
The diff coverage is 71.87%.

❗ Current head 1922f60 differs from pull request most recent head 8ed98b2. Consider uploading reports for the commit 8ed98b2 to get more accurate results

@@            Coverage Diff             @@
##             main      #55      +/-   ##
==========================================
+ Coverage   91.51%   91.59%   +0.07%     
==========================================
  Files          45       45              
  Lines        1132     1142      +10     
==========================================
+ Hits         1036     1046      +10     
  Misses         96       96              

Impacted Files	Coverage Δ
src/safeds/data/tabular/_column.py	89.84% <62.50%> (+0.32%)	⬆️
src/safeds/data/tabular/_row.py	72.00% <100.00%> (+3.81%)	⬆️
src/safeds/exceptions/_data_exceptions.py	96.29% <100.00%> (ø)

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[lars-reimann]

🎉 This PR is included in version 0.3.0 🎉

The release is available on:

• v0.3.0
• GitHub release

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