Apply enacted treasury withdrawals

[aniketd]

Description

Closes #3736

Also add lenses ensWithdrawalsL, ensTreasuryL and epochStateTreasuryL.

Checklist

• Commit sequence broadly makes sense and commits have useful messages
• New tests are added if needed and existing tests are updated
• When applicable, versions are updated in .cabal and CHANGELOG.md files according to the
  versioning process.
• The version bounds in .cabal files for all affected packages are updated. If you change the bounds in a cabal file, that package itself must have a version increase. (See RELEASING.md)
• All visible changes are prepended to the latest section of a CHANGELOG.md for the affected packages. New section is never added with the code changes. (See RELEASING.md)
• Code is formatted with fourmolu (use scripts/fourmolize.sh)
• Cabal files are formatted (use scripts/cabal-format.sh)
• hie.yaml has been updated (use scripts/gen-hie.sh)
• Self-reviewed the diff

[aniketd]

This needs a bit of rework (potential underflow and some known guarantees).

[lehins]

You are still missing some parts from the spec, like this one:
https://github.com/input-output-hk/formal-ledger-specifications/blob/d8260e001e248725a01335253ce33f35d1656fe7/src/Ledger/Chain.lagda#L84

We'll talk more about it during the meeting, but I think you haven't looked deeply into how ensTreasury field works in EnactState and how it relates to `epochStateTreasuryL

[lehins]

Perfect! 👍