feat(boojum): FRI prover changes from boojum-integration (#187)

# What ❔

`prover/` directory changes from boojum-integration branch

## Why ❔

To make the diff smaller

## Checklist

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- [ ] PR title corresponds to the body of PR (we generate changelog
entries from PRs).
- [ ] Tests for the changes have been added / updated.
- [ ] Documentation comments have been added / updated.
- [ ] Code has been formatted via `zk fmt` and `zk lint`.