Add Parallel WaveGAN generator

[Yuan-ManX]

✨ Description

[Please describe the background, purpose, changes made, and how to test this PR]

🚧 Related Issues

[List the issue numbers related to this PR]

👨‍💻 Changes Proposed

• [ ] change1
• [ ] ...

🧑‍🤝‍🧑 Who Can Review?

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🛠 TODO

• [ ] task1
• [ ] ...

✅ Checklist

• [ ] Code has been reviewed
• [ ] Code complies with the project's code standards and best practices
• [ ] Code has passed all tests
• [ ] Code does not affect the normal use of existing features
• [ ] Code has been commented properly
• [ ] Documentation has been updated (if applicable)
• [ ] Demo/checkpoint has been attached (if applicable)

[lmxue]

Please refine and enhance the content related to PR, such as Description, Changes Proposed. And also make sure the code is formatted by 'black' formatter, as described in here.

Additionally, please provide the final checkpoints and samples.