[jtc] Improve trajectory sampling efficiency (backport #1297)

[mergify]

This PR addresses the increasing effort required in Trajectory::sample() raised in #1293 by exploiting the monotonically increasing access time for any trajectory. Instead of scanning through the complete trajectory to find the relevant trajectory points for the current sampling time, the Trajectory class keeps track of the last accessed index and only searches from there on. This supersedes the proposed binary search in #1294 and is based on #474.

Based on the requests in #474, i added checks for the new trajectory state to existing tests and added a new test to make sure that the index is correctly reset when calling Trajectory::update(). I verified that this indeed solves the problem by re-running the trajectory from #1293 and again plotting the periods between write() calls in my hardware interface:

The upper plot shows the progression of the period before this change, the lower one the behavior wtih this PR applied. The large spikes at the beginning and end are the start and end of the trajectory, the spikes in the middle are probably a result of me testing this on my normal laptop without RT kernel and doing some things on the side.

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This is an automatic backport of pull request #1297 done by Mergify.

[codecov]

Codecov Report

Attention: Patch coverage is 44.08602% with 52 lines in your changes missing coverage. Please review.

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Files with missing lines	Patch %	Lines
...int_trajectory_controller/test/test_trajectory.cpp	40.90%	0 Missing and 52 partials ⚠️

Additional details and impacted files

@@            Coverage Diff            @@
##             humble    #1357   +/-   ##
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  Coverage          ?   65.03%           
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  Files             ?      107           
  Lines             ?    12374           
  Branches          ?     7666           
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  Hits              ?     8047           
  Misses            ?     1555           
  Partials          ?     2772           

Flag	Coverage Δ
unittests	65.03% <44.08%> (?)

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Files with missing lines	Coverage Δ
...include/joint_trajectory_controller/trajectory.hpp	76.47% <100.00%> (ø)
joint_trajectory_controller/src/trajectory.cpp	90.40% <100.00%> (ø)
...int_trajectory_controller/test/test_trajectory.cpp	63.27% <40.90%> (ø)