[Off-chain] Consolidate and expose off-chain persistence

[bryanchriswhite]

Objective

Consolidate all off-chain persistent storage into a single "multi-store".

Origin Document

Goals

• Eliminate feature-specific and/or generally duplicated off-chain persistence artifacts.
• Provide an conventional pathway for new features to integrate with off-chain persistence.
• Minimize maintenance and operational complexity.

Deliverables

• A PR which adds a generic, off-chain, "multi-store" persistence interface and initial implementation using existing off-chain persistence tooling (badgerdb, I think).
• A PR which adds developer documentation detailing how to use the multi-store to add and interact with a new sub-store.
• A PR(s) which consolidate(s) existing off-chain persistence to "multi-store" usage.

Non-goals / Non-deliverables

• Refactoring existing persistence logic or mechanisms beyond what is necessary to achieve the outlined goals.

General deliverables

• Comments: Add/update TODOs and comments alongside the source code so it is easier to follow.
• Testing: Add new tests (unit and/or E2E) to the test suite.
• Makefile: Add new targets to the Makefile to make the new functionality easier to use.
• Documentation: Update architectural or development READMEs; use mermaid diagrams where appropriate.

---

Creator: @bryanchriswhite
Co-Owners: @red-0ne