Optimized HeartLib Notebook for Colab/Kaggle

[theelderemo]

This PR adds two files to the notebooks directory:

1. heartlib.py: A standalone Python script for inference.
2. HeartLib.ipynb: A Colab notebook that demonstrates usage.

In PR #49 (great work btw) I noticed the discussion regarding the maintenance burden of notebooks. Including the raw Python script (heartlib.py) alongside the notebook solves this by allowing logic to be tracked and diffed easily in a standard code format.

#49 covers basic Colab functionality, this might complement it, focusing heavily on optimization and includes:

• Flash Attention integration for A100 GPUs
• Auto adjusting output length based on lyrics
• Support for both Colab and Kaggle

I understand you're considering external links over in-repo files per the discussion. Feel free to:

• Cherry pick any useful parts
• Just link to my Colab with the script or to just my repo with the notebook files if you prefer
• Merge this if the extra features are helpful
• Close if redundant

or whatever serves the project best. The idea is making HeartLib more accessible to everyone regardless of hardware constraints. I could care less about credit.

Happy to iterate on this if you prefer a different structure