Add FS2S
This pull request **introduces 2 alerts** when merging 900c52a2fc5e01c04dddb29d51b3894c504e837b into 45aaaf4aad712d53b58e6b14db6343c4e9940f25 - [view on LGTM.com](https://lgtm.com/projects/g/NVIDIA/NeMo/rev/pr-3758cb3dc44cd572ab179a17194a1cafa9166522)

**new alerts:**

* 2 for Unused import This pull request **introduces 2 alerts** when merging ed9d82b7a6032b7304e436434c0c6e78eff6e983 into 2b0711778f3463188ea87bdfd1b0b4ecc48ec11a - [view on LGTM.com](https://lgtm.com/projects/g/NVIDIA/NeMo/rev/pr-f13ab895beee0599ab6d003ce727ebb54e1dc13c)

**new alerts:**

* 2 for Unused import This pull request **introduces 6 alerts** and **fixes 3** when merging fd12af9df4dacabd9125780096e4894df72d3fd3 into 2b0711778f3463188ea87bdfd1b0b4ecc48ec11a - [view on LGTM.com](https://lgtm.com/projects/g/NVIDIA/NeMo/rev/pr-a88f3b11a7402e4cda247156a26cc184b2d2cd9f)

**new alerts:**

* 6 for Unused import

**fixed alerts:**

* 3 for Unused import This pull request **fixes 5 alerts** when merging c0c4b099004111aad1369cb2d8dc0279262f223a into 2b0711778f3463188ea87bdfd1b0b4ecc48ec11a - [view on LGTM.com](https://lgtm.com/projects/g/NVIDIA/NeMo/rev/pr-53f33ff6e93e839ad537f3d533f1298f69698046)

**fixed alerts:**

* 5 for Unused import This pull request **fixes 5 alerts** when merging 6d082c04ce7cf0265b4e3d6f50f5581b1967e8b0 into 2b0711778f3463188ea87bdfd1b0b4ecc48ec11a - [view on LGTM.com](https://lgtm.com/projects/g/NVIDIA/NeMo/rev/pr-5bc4526daea285700462f767ea9bb14afb250381)

**fixed alerts:**

* 5 for Unused import
- [x] Merge with main
- [x] Use HiFiGAN modules
- [x] Use our FS2 modules