Added clear, clear_edges functions to PyGraph and PyDiGraph objects

[abhamra]

Can now use clear() and clear_edges() on any PyGraph or PyDiGraph object, fixes #984.
clear(): Clears all nodes and edges, updates node_removed value to true
clear_edges(): Clears all edges, leaves nodes intact.

[IvanIsCoding]

Overall this LGTM, I think we just need to add another test and it should be good to go

[abhamra]

@IvanIsCoding Just put in a commit that adds graph reuse cases for both clear() and clear_edges(), let me know if anything else needs fixing and thank you for the feedback!

[mtreinish]

The CI failures you hit before were caused by the new release of rust that happened today: https://blog.rust-lang.org/2023/10/05/Rust-1.73.0.html

I pushed up a separate PR to fix these build errors: #996

[abhamra]

Copy that @mtreinish, I pushed those fixes on my end since the issue you reference seems to have been merged.

[coveralls]

Pull Request Test Coverage Report for Build 6426717105

• 14 of 14 (100.0%) changed or added relevant lines in 2 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+0.003%) to 96.497%

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Totals
Change from base Build 6425158600:	0.003%
Covered Lines:	15428
Relevant Lines:	15988

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💛 - Coveralls

[abhamra]

@mtreinish @IvanIsCoding Thank you for the help with my first PR!

[IvanIsCoding]

Congrats on your first contribution to rustworkx!