* 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
