feat(relay): add maxTotalEventsPerReq to cap aggregate events across filters

[Thunder-Blaze]

Description

• maxFilterLimit caps the events returned by each individual filter (default 500), but a REQ with many filters can return maxReqFilterSize * maxFilterLimit events (e.g. 200 * 500 = 100,000). There's no aggregate cap.

• This adds relay.maxTotalEventsPerReq (default 0 = unlimited). When set, the total events sent across all filters in a single REQ is capped. Once the limit is hit, remaining filters are skipped and a warning is logged. The client still receives a normal EOSE.

Issue

• Listed in TODO file (rate limits section)

Testing

• Builds and runs as expected

Custom tests

[hoytech]

Good idea, thanks! I wonder if we should put a default in, instead of unlimited? Can you maybe start a discussion in the TG channel about this? My instinct would be something like 2000 or so.