Update tracking_metrics.py

[lanery]

Change definition of max_sprint_length to be calculated as a rolling sum (to better match the tracks in the animations). Facilitates interpretation of this measurement. num_direction_changes (and therefore also pivot_rate) are also changed to be defined as rolling averages, but more so to suppress noise in the trajectory.

Pretty much summed up in the commit message

Change definition of `max_sprint_length` to be calculated as a rolling sum (to better
match the tracks in the animations). Facilitates interpretation of this measurement.
`num_direction_changes` (and therefore also `pivot_rate` are also changed to be defined
as rolling averages, but more so to suppress noise in the trajectory.

Have not yet taken the time to write integration tests, but have re-analyzed all of the useful motility data we have with these new definitions.

PR checklist

• Describe the changes you've made.
• Describe any tests you have conducted to confirm that your changes behave as expected.
• If you've added new functionality, make sure that the documentation is updated accordingly.