dynamically update user redemption records during unbonding

[sampocs]

Context

(See #1049 for more context)

Refactored the dynamic redemption rate during unbonding PR.

Motivation for refactoring:

• Further modularize functions to give more fine grained test coverage
• Explicitly separate steps that modify state vs those that are just doing calculations
• Put the new dynamic unbonding code as upstream as possible (so it's less invasive to the current unbonding code), while still keeping the native calculation and the unbonding ICAs atomic

[riley-stride]

Manual testing to inspect the native_token_amount incrementing: Here's a gist that shows native_token_amount incrementing on epoch-unbonding-records upon unbonding. CMD+F for "1004" to see native_token_amount increment. Note this change aligns with the status of the record changing to UNBONDING_IN_PROGRESS, as expected.

[riley-stride]

Unit tests look quite solid. Covering all the functions and edge cases I can think of. If we wanted to beef them up we could test RefreshHostZoneUnbondingNativeTokenAmount and RefreshUserRedemptionRecordNativeAmounts more directly, but I think RefreshHostZoneUnbondingNativeTokenAmount already has good coverage of these indirectly, as you noted.