chore: rai-perception - update docs to use pip install and add more tests

[Juliaj]

Purpose

Support #697

Proposed Changes

• Update rai-perception README to install package via pip
• Increase test coverage

Testing

• New unit test added.
• All tests run and passed.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 65.32%. Comparing base (a0addd0) to head (56c34e6).
✅ All tests successful. No failed tests found.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #719   +/-   ##
=======================================
  Coverage   65.32%   65.32%           
=======================================
  Files          78       78           
  Lines        3386     3386           
=======================================
  Hits         2212     2212           
  Misses       1174     1174           

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