[Architecture] Break circular references between core components

[bbopen]

Summary

Core components (Ledger, CRDT, Blockstore, Loader) have circular parent references that prevent garbage collection. This causes memory leaks when databases are opened and closed repeatedly.

Problem

The current architecture has:

• CRDT holds reference to Ledger
• Blockstore holds reference to CRDT
• Loader holds references to multiple components
• These circular references prevent cleanup when close() is called

Repeatedly opening and closing databases causes unbounded memory growth.

Proposed Solution

1. Define clean interfaces in core/types/:
   • ILedger, ICRDT, IBlockstore, ILoader
2. Extract responsibilities from monolithic Loader:
   • BlockLoader - block loading/caching
   • MetaLoader - metadata management
   • CompactionManager - compaction logic
3. Replace parent object references with IDs
4. Create ComponentRegistry for service lookup
5. Add event-based communication between components

Expected Outcomes

• Closing database releases all associated resources
• No references remain to closed database objects
• Components testable in isolation
• Memory stabilizes after 1000 open/close cycles

[bbopen]

PR #1502 addresses the first phase of this issue by fixing the immediate memory leak problem during database close.

What's Fixed

The PR resolves the "local store not set" errors that occurred when async operations (meta stream handler, write queue) continued running after close() was called. The root cause was reset() clearing _local = undefined too early while these async operations still needed the reference.

Changes

• Added localOrUndefined() method for safe access during teardown
• Modified reset() to preserve _local for async operations
• Updated destroy() to gracefully handle already-reset state

What's Next

The full architectural refactoring (interface extraction, Loader decomposition, ComponentRegistry) outlined in this issue would be follow-up work. This PR is a targeted fix for the immediate memory leak symptom.