feat: active filter subscription management for edge nodes
## Subscription Manager
* edgeFilterSubLoop reconciles desired vs actual filter subscriptions
* edgeFilterHealthLoop pings filter peers, evicts stale ones
* EdgeFilterSubState per-shard tracking of confirmed peers and health
* best-effort unsubscribe on peer removal
* RequestEdgeShardHealth and RequestEdgeFilterPeerCount broker providers
## WakuNode
* Remove old edge health loop (loopEdgeHealth, edgeHealthEvent, calculateEdgeTopicHealth)
* Register MessageSeenEvent push handler on filter client during start
* startDeliveryService now returns `Result[void, string]` and propagates errors
## Health Monitor
* getFilterClientHealth queries RequestEdgeFilterPeerCount via broker
* Shard/content health providers fall back to RequestEdgeShardHealth when relay inactive
* Listen to EventShardTopicHealthChange for health recalculation
* Add missing return p.notReady() on failed edge filter peer count request
* HealthyThreshold constant moved to `connection_status.nim`
## Broker types
* RequestEdgeShardHealth, RequestEdgeFilterPeerCount request types
* EventShardTopicHealthChange event type
## Filter Client
* Add timeout parameter to ping proc
## Tests
* Health monitor event tests with per-node lockNewGlobalBrokerContext
* Edge (light client) health update test
* Edge health driven by confirmed filter subscriptions test
* API subscription tests: sub/receive, failover, peer replacement
Co-authored-by: Ivan FB <128452529+Ivansete-status@users.noreply.github.com>
Co-authored by Zoltan Nagy
