Save the DRep Pulser State after computing it

[sgillespie]

Description

Fixes #1599. The bulk of this work is done in the HasNewEpochState typeclass, which allows us to update the ledger state in ExtLedgerState.

Checklist

• [x] Commit sequence broadly makes sense
• [x] Commits have useful messages
• [ ] New tests are added if needed and existing tests are updated
• [ ] Any changes are noted in the changelog
• [x] Code is formatted with fourmolu on version 0.10.1.0 (which can be run with scripts/fourmolize.sh)
• [x] Self-reviewed the diff

Migrations

• [ ] The pr causes a breaking change of type a,b or c
• [ ] If there is a breaking change, the pr includes a database migration and/or a fix process for old values, so that upgrade is possible
• [ ] Resyncing and running the migrations provided will result in the same database semantically

If there is a breaking change, especially a big one, please add a justification here. Please elaborate more what the migration achieves, what it cannot achieve or why a migration is not possible.

[sgillespie]

Great work! Good to merge when it's tested on preprod or preview.

It can't be tested in preprod or preview right?

Also, I forgot to update the comment, I have done some basic manual testing in sanchonet

[kderme]

It can't be tested in preprod or preview right?

Right, it would only work on sanchonet after rebasing to master

[sgillespie]

Right, it would only work on sanchonet after rebasing to master

Yes, this is how I was able to test it on sanchonet. I applied my changes on top of sancho-4-2-1