feat(state): control-plane store SPI + deprecate zombie code (#5301 Sub-PR A)

[qqeasonchen]

Sub-PR A: Control-plane store SPI + deprecate zombie code (issue #5301)

This is the first of four sub-PRs that deliver issue #5301
("Unified state control-plane stores"). Sub-PR A adds the SPI surface, adapts
two existing implementations to it, and deprecates three zombie-code classes
that the new architecture will eventually replace.

It does not change runtime behavior: nothing currently calls the new
interfaces yet (call sites move over in Sub-PRs B and C).

What's in this PR

New public interfaces (in org.apache.eventmesh.runtime.state)

Interface	Backed by (target)	Purpose
SubscriptionStore	Meta prefix-watch + local cache	Cluster-shared subscription registry
SessionStore	Meta prefix-watch + local cache	Cluster-shared agent / binding / session registry
DeadLetterStore	Meta CAS (idempotent)	Durable ledger of dead-lettered deliveries
TaskStore	Meta CAS + epoch-protected status transitions	A2A task state (with TTL via expireStale)

OffsetStore and DeliveryStateStore are intentionally not added in this
PR — they are introduced in Sub-PRs B and C with the actual storage backends.

Adapted implementations

• ClusterSubscriptionStore now implements SubscriptionStore. remove(...)
  returns the boolean result from Meta.delete(...) so callers can detect
  when a subscription was already gone (idempotent teardown).
• SessionRegistry now implements SessionStore. register/markReady/ unregister are renamed to registerAgent/markAgentReady/unregisterAgent
  to match the interface contract (no callers existed in the current tree
  for the old names).

Zombie code marked @Deprecated(forRemoval = true)

Pending issue #5309
("PARTITION_OWNED_PULL delivery topology"):

• cluster.PartitionOwnership — only callable from the second delivery mode
  the closed [Architecture Review][P0] Configurable DeliveryTopology for cluster delivery #5300 originally enabled; will return as part of [Architecture Review][P0] PARTITION_OWNED_PULL delivery topology (reopens #5300 second mode) #5309.
• cluster.ClusterCoordinator — superseded by the new Meta CAS path.
• cluster.MetaBackedOffsetStore — superseded by the OffsetStore in
  Sub-PR B.

Unit tests

SubscriptionStoreTest (5), SessionStoreTest (6), DeadLetterStoreTest
(2), TaskStoreTest (3) — total 16 tests, all in-process with hand-
rolled test doubles (no Nacos/RocksDB/Testcontainers needed). They pin the
SPI contract so subsequent sub-PRs can build on it.

Out of scope (handled in follow-up sub-PRs)

• Sub-PR B — DeliveryStateStore (RocksDB) + OffsetStore (Meta async
  flush); wire DeliveryStateStore into the new consumer path.
• Sub-PR C — DeadLetterStore Meta-backed implementation + TaskStore
  Meta-backed implementation; wire A2A TaskRegistry over TaskStore.
• Sub-PR D — fault-injection Testcontainers E2E covering partition
  transfer, Meta outage, DLQ replay, and TaskStore epoch conflict.

Open questions for the maintainer

(Inherited from the #5301 issue body — please review there.)

1. Should DeadLetterStore.recordDeadLetter carry a dlqOffset (current
   design), or just the dlqTopic so the offset is derived?
2. Should TaskStore.TaskRecord carry full input / output payloads, or
   only a payloadRef that points to a separate blob store?
3. For SubscriptionStore.put, do we want a separate putIfAbsent variant
   to make subscription reconciliation idempotent without overwriting?
4. Should the SessionStore interface include a Watch / Subscription
   callback hook (similar to Nacos Listener) so callers can react to
   session-state changes without polling?

Testing

This PR was developed on the uni-runtime branch (develop at
7260581). The full eventmesh-runtime:compileJava plus the four new
test classes pass locally with JDK 21 + Gradle 8.7. Upstream CI will be
the source of truth — if anything in the SPI needs to change, the four
sub-PRs are independent so a fix here will not block B/C/D.