Add unit tests for `Pose` class

[sea-bass]

The Pose class, found at pyrobosim/pyrobosim/utils/pose.py, is used all throughout pyrobosim and is in need of extensive unit tests.

When writing tests, pay close attention to:

• Object creation using the constructor or the static methods provided, especially testing optional arguments and things that conflict with each other (like Euler angles vs. quaternions)
• Utilities to get matrices, Euler angles, quaternions, etc. from a Pose
• Comparison utilities to calculate linear and angular distances