Changing usages of index(t) to a more robust isclose()

[robotAstray]

Summary

This PR addresses issue #11 . The PR replaces the usage of index(t) with a more robust approach using np.isclose() in the plot_routines.py

Details and Comments

• Replaced instances of index(t) with a new function called find_index_nearest_time_within_tolerance(), utilising np.isclose(). This change ensures more accurate and reliable time comparisons.

• Introduced the rtol parameter to the find_index_nearest_time_within_tolerance() function, offering control over the relative precision used in time comparisons.