[Performance] Implement Memory-Mapped (mmap) Poller Cache

[somethingwithproof]

Summary

Spine currently executes thousands of SELECT queries against the database at the start of a poll cycle to determine the 'previous state' and metadata of a host.

Work

• Replace the SQL-backed state cache with a Shared Memory (mmap) segment or a lightweight embedded datastore (like LMDB or LevelDB).
• Architecture: The 'Live' poller state is kept in memory. Spine reads/updates this instantly with zero network overhead.
• Dependency: This requires coordination with the upstream Cacti PHP application so the UI can read the shared memory state instead of querying the SQL host table.
• Performance Gain: Near-instant host status lookups and a massive reduction in read queries against the main database.

Acceptance Criteria

• Work items are implemented and validated.
• Changes preserve behavior unless explicitly intended.