Shared handle to a live admission queue. Holds the manager (for spawning a
fresh per-epoch actor on reconfig), the per-epoch ArcSwap handle, and the
cached (config-derived) bypass threshold. Cloned cheaply by Arc; passed
both to ValidatorService (for hot-path routing) and through
ValidatorComponents (for epoch rotation).
Manages the lifecycle of per-epoch admission queue actors.
Holds immutable config and shared metrics; call spawn() each epoch
with the new epoch store to create a fresh actor and handle.
Bounded priority queue that orders transactions by gas price. Uses a BTreeMap
for efficient access at both ends: lowest gas price (for eviction) and highest
gas price (for draining to consensus). Entries at the same gas price are FIFO.