Add Unit Tests for Bitcrush Plugin

[Anipaleja]

This pull request adds a dedicated test suite for the Bitcrush plugin to enhance test coverage and improve long-term stability.

Changes:

• Changed tests/test_bitcrush.py
• Added tests for:
  • Basic audio transformation with a sine wave input
  • Edge cases (bit depths of 1 and 24)
  • Invalid input handling (e.g., negative or excessively high bit depth)

Rationale:
These tests ensure the Bitcrush plugin behaves as expected under normal and extreme conditions. They also verify that invalid configurations correctly raise exceptions, helping maintain robustness and usability.

All tests pass locally using pytest. Let me know if you'd like any additional coverage or formatting changes!