Proto: store slashed deposits history

/!\ Based on !8753 (merged), the first commit of this MR is Proto/Storage: add slashed deposits history

Context

To compute the real value of costake withdrawals we need to be able to apply slashing percentages to uncostake requested amounts, hence we need to store these percentages.

This is done in a manner that is efficient in practice (a single associative list per account rather than a map), because there are no slashings, but would be inefficient if there were many.

Manually testing the MR

It should have no impacts today and will be tested together with uncostake withdrawals.

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).
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