Add time-domain IR render and utility functions

[SebastianJiroSchlecht]

Add build_impulse_response for time-domain FDN rendering (avoids FFT aliasing), fade_out for linear tail attenuation, and labeled_audio for marimo A/B listening layouts. Rename with_decay to build_set_decay for clarity. Update example notebook to use the new functions and simplify audio rendering code.

Summary

Fixes #

Changes

Testing

• pytest passes locally
• New tests added for new functionality
• Coverage not decreased (pytest --cov=pyFDN)

Checklist

• Pre-commit hooks pass (pre-commit run --all-files)
• Docstrings updated for any changed public API
• HISTORY.rst updated if this is a user-facing change

[jeremybbq]

Name suggest.

[SebastianJiroSchlecht]

@jeremybbq Thanks for checking the PR. Please go ahead with the merge (once the CI passes)