test: snapshot tests

[lars-reimann]

Closes #482
Closes #483

Summary of Changes

• Use sypury snapshot tests for images. Run pytest --snapshot-update to update snapshots after changes.
• Fix random test failures due to TCL when running tests in a terminal

[github-actions]

🦙 MegaLinter status: ✅ SUCCESS

Descriptor	Linter	Files	Fixed	Errors	Elapsed time
✅ PYTHON	black	9	0	0	0.63s
✅ PYTHON	mypy	9		0	1.41s
✅ PYTHON	ruff	9	0	0	0.08s
✅ REPOSITORY	git_diff	yes		no	0.07s

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[lars-reimann]

@Gerhardsa0 please check whether you can now run the tests without random errors.
@Safe-DS/library I would appreciate it if one of you could review this.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (6443beb) 100.00% compared to head (82de801) 100.00%.

Additional details and impacted files

@@            Coverage Diff            @@
##              main      #495   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files           49        49           
  Lines         2699      2699           
=========================================
  Hits          2699      2699           

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[lars-reimann]

🎉 This PR is included in version 0.16.0 🎉

The release is available on:

• v0.16.0
• GitHub release

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