[WIP] Various Improvements

[Eric-Vin]

Description

Placeholder PR to track various Scenic improvements.

Driving Domain Behaviors:

• Added a pure pursuit lateral controller, which performs far better than the PID lateral controller.

General Improvements:

• Added apparent heading to X [from Y] scalar operator along with X ahead of Y, X behind Y, X left of Y, and X right of Y boolean operators.
• Added support for running behaviors in parallel.
• Added a new followFromTrajectory method which returns the entire trajectory followed instead of just the final point.
• Scenic now detects changes to the parser and will automatically re-build it when needed.

Bugfixes:

• Fixed order of lanes in backwards LaneGroup. Previously, backwards lane groups had this tuple in the opposite direction (element 0 farthest from the curb).

Issue Link

NA

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)

Additional Notes

NA

[codecov]

Codecov Report

❌ Patch coverage is 61.13208% with 103 lines in your changes missing coverage. Please review.
✅ Project coverage is 87.66%. Comparing base (4be87bd) to head (7bc9cbc).
⚠️ Report is 4 commits behind head on main.

Files with missing lines	Patch %	Lines
src/scenic/core/serialization.py	6.15%	61 Missing ⚠️
src/scenic/domains/driving/controllers.py	62.66%	28 Missing ⚠️
src/scenic/syntax/__init__.py	66.66%	5 Missing ⚠️
src/scenic/syntax/veneer.py	83.33%	5 Missing ⚠️
src/scenic/domains/driving/actions.py	55.55%	4 Missing ⚠️

❌ Your patch check has failed because the patch coverage (61.13%) is below the target coverage (80.00%). You can increase the patch coverage or adjust the target coverage.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #487      +/-   ##
==========================================
- Coverage   89.85%   87.66%   -2.20%     
==========================================
  Files          48       48              
  Lines       13346    13553     +207     
==========================================
- Hits        11992    11881     -111     
- Misses       1354     1672     +318     

Files with missing lines	Coverage Δ
src/scenic/core/dynamics/behaviors.py	96.22% <100.00%> (+0.39%)	⬆️
src/scenic/core/object_types.py	91.07% <100.00%> (-2.09%)	⬇️
src/scenic/core/simulators.py	83.86% <100.00%> (-11.99%)	⬇️
src/scenic/core/vectors.py	87.95% <100.00%> (-0.80%)	⬇️
src/scenic/domains/driving/roads.py	94.54% <100.00%> (ø)
src/scenic/formats/opendrive/xodr_parser.py	92.70% <ø> (ø)
src/scenic/syntax/ast.py	97.32% <100.00%> (+0.12%)	⬆️
src/scenic/syntax/compiler.py	98.17% <100.00%> (-0.11%)	⬇️
src/scenic/domains/driving/actions.py	69.02% <55.55%> (-10.61%)	⬇️
src/scenic/syntax/__init__.py	73.52% <66.66%> (-6.48%)	⬇️
... and 3 more

... and 7 files with indirect coverage changes

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