Proto: new implementation of min delegated in cycle

Based on !14041 (merged).

This MR implements a new semantics of min-delegated-in-cycle that only consider values in between blocks.

See this doc for visualization of tests.

Manually testing the MR

dune exec src/proto_alpha/lib_protocol/test/unit/main.exe -- --file test_full_staking_balance_repr.ml --info

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, CHANGES.rst at the root of the repository for everything else).
• Select suitable reviewers using the Reviewers field below.
• Select as Assignee the next person who should take action on that MR