Add Topology.clear_positions

[mattwthompson]

This adds Topology.clear_positions() which does what the name implies, instead of allowing Topology.set_positions(None) as I originally advocated for in #1820. Today I think it's better to just have a separate method that does this one thing - it handles what I remember my use case to be - instead of allowing set_positions to take different types.

I hold this preference weakly (I've already changed my mine once on my own) and can easily be talked out of it

• Tag issue being addressed
• Add tests
• Update docstrings/documentation, if applicable
• Lint codebase
• Update changelog

[codecov]

Codecov Report

Merging #1827 (0fb80b0) into main (118918c) will increase coverage by 0.00%.
The diff coverage is 100.00%.

Additional details and impacted files

[j-wags]

Excellent. Thanks @mattwthompson!