fix all JUCE deprecation warnings; update pre-commit hooks

- Add MidiBufferCursor in ProcessorBase.h replacing the deprecated
  juce::MidiBuffer::Iterator in FaustProcessor, PluginProcessor, and
  SamplerProcessor
- Replace deprecated AudioProcessor::getNumParameters/getParameterName/
  getParameter/getParameterText with the getParameters() array API;
  out-of-range parameter indices now raise instead of returning ''
- Use the Attributes form of the AudioParameterFloat constructor
- Remove Source/RenderEngine.h.backup
- pre-commit autoupdate; fix the .jucer exclude regex (double backslash
  never matched); skip .ipynb in codespell; ruff -> ruff-check
- The Linux Release build now compiles with zero warnings