Proto: SCORU: Commitment logic

Add API to Sc_rollup_storage and Alpha_context.Sc_rollup for manipulation of pending commitments. Specifically this API adds protocol functions for:

• Submitting and withdrawing stake.
• Staking one new commitments.
• Staking on previous commitments.
• Extraction of conflict points for dispute starts.
• Forced removal of stakers, intended to be used at dispute conclusion.

Adds the following tests (in test_sc_rollup_storage.ml):

• Deposit to missing rollup fails.
• Deposit to existing rollup succeeds.
• Deposit, then withdrawing succeeds.
• Withdrawing when not staked fails.
• Withdrawing twice fails.
• Staking on a new node succeeds.
• Staking on existing node succeeds.
• Withdrawal fails when not staked on LFC.
• Rollup starts in pre-boot state.
• Finalization succeeds.
• Finalization fails when the commitment is too recent.
• Finalization with two stakers succeeds.
• Finalization fails on conflict.
• We can finds a conflict point at the LFC.
• We can force-remove stakers.
• A removed staker can not withdraw.
• Removing a staker from the LFC fails.

I'm planning to add further tests, tracked in #2460.

Context

This follows !4148 (merged), implementing commitment logic for Smart Contract Optimistic Rollups.

Actual handling of stake amounts (debit/credit/freezing) is not implemented here. This is tracked in #2449 (closed).

Fixes #2106 (closed) #2117 (closed) #2113 (closed)

Manually testing the MR

dune exec src/proto_alpha/lib_protocol/test/unit/main.exe  -- test "^\[Unit\] Sc_rollup_storage.ml$"

Checklist

• Document the interface of any function added or modified (see the coding guidelines)
• Document any change to the user interface, including configuration parameters (see node configuration)
• Provide automatic testing (see the testing guide).
• For new features and bug fixes, add an item in the appropriate changelog (docs/protocols/alpha.rst for the protocol and the environment, the Development Version section of CHANGES.md for everything else).
• Select suitable reviewers using the Reviewers field below.
• Select as Assignee the next person who should take action on that MR