refactor(sequencer): provide storage and snapshot types

[Fraser999]

Summary

This adds new storage types to sequencer and replaces bare usage of cnidarium equivalent types.

Background

We want to become less coupled to the raw cnidarium APIs, and we also want to provide a cache of recently-read values.

Changes

• Provided new storage::Storage type, wrapping the cnidarium::Storage type.
• Provided new storage::Snapshot type, wrapping the cnidarium::Snapshot type and including a cache of fetched values.
• When the sequencer main loop has finished, we now await the server handle and then call storage.release().await; which should probably have been the case before this PR.
• Applied consistent naming to variables of type StateDelta<Snapshot> and StateDelta<StateDelta<Snapshot>>.

Testing

Added unit tests for the new types covering the non-trivial methods (many new methods simply call directly through to the equivalent inner method and don't need independent unit tests).

Changelogs

Changelogs updated.

Metrics

• Added astria_sequencer_verifiable_cache_hit counter
• Added astria_sequencer_verifiable_cache_miss counter
• Added astria_sequencer_verifiable_cache_item_total histogram
• Added astria_sequencer_non_verifiable_cache_hit counter
• Added astria_sequencer_non_verifiable_cache_miss counter
• Added astria_sequencer_non_verifiable_cache_item_total histogram

Related Issues

Closes #1435.