Various OpenDRIVE fixes

[dfremont]

Description

Fixes various bugs with the OpenDRIVE parser and makes it more robust to some issues in maps we've been sent. In particular:

• fix code that ensures we generate vertices at transtions between geometries (thanks @Eric-Vin for implementing this)
• tolerate negative lane widths
• tolerate zero-width portions of lanes (by eliding them)
• only clean polygons if they are invalid (our prior eager approach sometimes unnecessarily corrupted very thin lanes)
• fix differencing of adjacent lane polygons
• skip spirals with very high curvature rates (which are probably artifacts)
• simplify and improve code for skipping suspicious geometries
• lane overlap removal shrinks the larger lane
• fix combineSections logic for sidewalks/shoulders so that left and right edges are properly computed (there are still issues with dropping certain parts of these regions, particularly on one-way roads, but the fix will require changes to the roads API so I'm deferring that)
• tolerate linkage to junctions missing corresponding connections

Thanks @Eric-Vin for independently fixing some of these bugs in #193.

Issue Link

Fixes #189. Fixes #274. Fixes #459.

Checklist

• I have tested the changes locally via pytest and/or other means
• I have added or updated relevant documentation
• I have autoformatted the code with black and isort
• I have added test cases (if applicable)

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 89.78%. Comparing base (62da37a) to head (9fc566b).

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #468      +/-   ##
==========================================
+ Coverage   89.70%   89.78%   +0.07%     
==========================================
  Files          48       48              
  Lines       13287    13322      +35     
==========================================
+ Hits        11919    11961      +42     
+ Misses       1368     1361       -7     

Files with missing lines	Coverage Δ
src/scenic/formats/opendrive/xodr_parser.py	92.04% <100.00%> (+0.54%)	⬆️

... and 2 files with indirect coverage changes

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