Merge branch 'feat/events-sse-endpoint' into feat/events-topics-filter

Adopt #517's beacon-aligned ChainEvent ({slot, block, state}, Serialize
derived on the type) while keeping #518's TopicSet/EventSubscription
filtering. The snapshot tests moved from lib.rs into events.rs upstream;
take that version and add TopicSet::ALL to their subscribe calls.

Update the topic-filter tests to the new field names, and switch the
"block filtered out" assertion to check the SSE event: line since every
payload now carries a `block` field.

Author: MegaRedHand

Cargo.lock

@@ -18,6 +18,7 @@ ethlambda-fork-choice.workspace = true
 ethlambda-crypto.workspace = true
 ethlambda-metrics.workspace = true
 ethlambda-types.workspace = true
+ethlambda-test-fixtures.workspace = true
 
 libssz.workspace = true
 
@@ -27,15 +28,13 @@ tokio.workspace = true
 tokio-util = { version = "0.7", default-features = false }
 
 rayon.workspace = true
+serde.workspace = true
 thiserror.workspace = true
 tracing.workspace = true
-serde.workspace = true
 
 hex.workspace = true
 
 [dev-dependencies]
-ethlambda-test-fixtures.workspace = true
-serde_json = { workspace = true }
 hex = { workspace = true }
 libssz.workspace = true
 libssz-types.workspace = true