Fix/pixel size type hint

[MaksHess]

Removed the overloaded type hints, assuming this is the intended behaviour:

axis exists -> float
axis does not exist, default: float -> float
axis does not exist, default = None -> raises

Checklist before merging

• I added an appropriate entry to CHANGELOG.md

No entry required IMO

[lorenzocerrone]

Good catch :)

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.

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