feat: add UTxO events query and pagination support to state queries

[whankinsiv]

Description

This PR adds UtxoEventsRequest which will be used as an alternative to the 4 separate query calls needed by the MidnightCNightObservationDataSource trait in midnight-node. This allows us to do server side sorting and capacity limiting, significantly simplifying the client side implementation.

Related Issue(s)

Relates to #734

How was this tested?

• Added unit tests for sorting, truncation, and getter capacity limitations

Checklist

• My code builds and passes local tests
• I added/updated tests for my changes, where applicable
• I updated documentation (if applicable)
• branch has ≤ 5 commits (honor system)
• commit messages tell a coherent story
• branch is up to date with main (rebased on main; fast-forward possible)
• CI/CD passes on the merged-with-main result

Impact / Side effects

Adds a new request handler and refactors the existing asset and candidate getters to return based on a provided capacity parameter.

Reviewer notes / Areas to focus

Sorting and truncation logic in modules/midnight_state/src/grpc/utxo_events.rs

[lowhung]

Looks good! Just some comments about the .expect(...) and test names.