fix: make multi-processing in baseline models more consistent

[sibre28]

Closes #907

Set Context of ProcesspoolExecutors to spawn

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🦙 MegaLinter status: ✅ SUCCESS

Descriptor	Linter	Files	Fixed	Errors	Elapsed time
✅ PYTHON	black	2	0	0	1.07s
✅ PYTHON	mypy	2		0	3.01s
✅ PYTHON	ruff	2	0	0	0.4s
✅ REPOSITORY	git_diff	yes		no	0.67s

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[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 97.77%. Comparing base (d3f81dc) to head (7e40c7b).

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #909 +/- ## ======================================= Coverage 97.77% 97.77% ======================================= Files 122 122 Lines 6592 6594 +2 ======================================= + Hits 6445 6447 +2 Misses 147 147 ```

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[lars-reimann]

:tada: This PR is included in version 0.27.0 :tada:

The release is available on:

• v0.27.0
• GitHub release

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