chore!: replace NMTProof with Proof in nmt

[Eoous]

Description

Use Proof in nmt instead of NMTProof.

Changed Makefile for removing protobuf file generated by buf.

Resolves #1429

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PR checklist

• [x] Tests written/updated
• [ ] Changelog entry added in .changelog (we use unclog to manage our changelog)
• [ ] Updated relevant documentation (docs/ or spec/) and code comments

[Eoous]

Currently it's not possible to exclude files via buf.yaml or other config files

[Eoous]

what's the status here? @Eoous

I have replaced it and need to review