protocol environment: Expose BLS signature module

Context

Exposes the Signature module to the environment v4 from the new bls12-381 bindings to blst. This is the simplest solution I could think of but we might want to constrain what is exposed in a future commit when we know more what is needed from the final Optimistic Rollups code.

Since we're not doing anything fancy with the bindings I decided to not add tests and trust the upstream library that should have been testet already since we already depend on it.

Closes #1646 (closed)

Manually testing the MR

Checklist

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