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
* SubscriptionManager tracks shard and content topic interest
* RecvService emits MessageReceivedEvent on subscribed content topics
* Route MAPI through old Kernel API relay unique-handler infra to avoid code duplication
* Encode current gen-zero network policy: on Core node boot, subscribe to all pubsub topics (all shards)
* Add test_api_subscriptions.nim (basic relay/core testing only)
* Removed any MAPI Edge sub/unsub/receive support code that was there (will add in next PR)
* Hook MessageSeenEvent to Kernel API bus
* Fix MAPI vs Kernel API unique relay handler support
* RecvService delegating topic subs to SubscriptionManager
* RecvService emits MessageReceivedEvent (fully filtered)
* Rename old SubscriptionManager to LegacySubscriptionManager
* bump_dependencies.md: add nim-results dependency
* change imports stew/results to results
* switching to Nim 2.0.8
* waku.nimble: reflect the requirement nim 1.6.0 to 2.0.8
Adding --mm:refc as nim 2.0 enables a new garbage collector that we're
not yet ready to support
* adapt waku code to Nim 2.0
* gcsafe adaptations because Nim 2.0 is more strict
