lmrpc: Maintain local piecerefs

[magik6k]

This should fix all known issues with PiecePark

• When pieces-refs are created but fail to park, piece refs will now get removed correctly
  • This also fixes the issue when the PiecePark task can fail with EOF.. due to stale URLs in stale piece_refs
• Don't assume that data is only read from the first piece
• Correctly remove piece_refs which don't end up added to a sector
• Cleanup orphaned piece_refs on startup
  • This should cleanup all mess accumulated by existing nodes
• Fix an edge-case where a piece_ref could be added to a piece which is currently getting removed

[magik6k]

NOTE: This PR won't land in main, but will be open until we land Curio-native markets.

Curio markets won't require this fix, and it is a little conflicting