Add Stopwatch class to replace Timer

[jslee02]

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Before creating a pull request

• Document new methods and classes
• Format new code files using ClangFormat by running make format
• Build with -DDART_TREAT_WARNINGS_AS_ERRORS=ON and resolve all the compile warnings

Before merging a pull request

• Set version target by selecting a milestone on the right side
• Summarize this change in CHANGELOG.md
• Add unit test(s) for this change

[codecov]

Codecov Report

Merging #1638 (bb5834b) into main (8eb7688) will increase coverage by 0.04%.
The diff coverage is 68.64%.

@@            Coverage Diff             @@
##             main    #1638      +/-   ##
==========================================
+ Coverage   58.96%   59.00%   +0.04%     
==========================================
  Files         485      488       +3     
  Lines       40272    40390     +118     
==========================================
+ Hits        23746    23832      +86     
- Misses      16526    16558      +32     

Impacted Files	Coverage Δ
dart/common/Stopwatch.cpp	19.44% <19.44%> (ø)
dart/common/detail/Stopwatch-impl.hpp	86.66% <86.66%> (ø)
python/dartpy/common/Stopwatch.cpp	100.00% <100.00%> (ø)
python/dartpy/common/module.cpp	100.00% <100.00%> (ø)
dart/dynamics/EulerJoint.cpp	73.09% <0.00%> (+2.92%)	⬆️