Measure bloom filter AppGossip hit rate

[yacovm]

Why this should be merged

It can be insightful to measure how effective and efficient is our gossip pull mechanism that is based on bloom filters.

How this works

This commit adds a metric to measure the bloom filter hit rate % for the gossip pull queries.

How this was tested

• Updated TestGossiperGossip accordingly to reflect the metrics
• Ran a modified avalanchego node and installed prometheus and grafana and observed the following:

Need to be documented in RELEASES.md?

No.

[Copilot]

Pull Request Overview

This PR adds instrumentation to measure the effectiveness of the bloom filter used in the gossip pull mechanism.

• Track and compute bloom filter hits and misses in AppRequest
• Introduce a bloomFilterHitRate histogram in the metrics and register it
• Extend unit tests to cover the new histogram and the computeBloomFilterHitPercentage function

Reviewed Changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated no comments.

File	Description
network/p2p/gossip/handler.go	Count filter hits/misses and compute hit percentage
network/p2p/gossip/gossip.go	Add bloomFilterHitRate histogram and register it
network/p2p/gossip/gossip_test.go	Update tests to assert metric observation and new logic

Comments suppressed due to low confidence (3)

network/p2p/gossip/gossip.go:115

• [nitpick] Metric name bloomfilter_hit_rate is inconsistent with the project’s snake_case convention; consider renaming to bloom_filter_hit_rate or prefixing with gossip_ to match other metric names.

			Name:      "bloomfilter_hit_rate",

network/p2p/gossip/gossip_test.go:633

• [nitpick] Consider adding tests for the error branches in computeBloomFilterHitPercentage (e.g., when safemath.Add or Mul overflows) to verify that ok is false in those cases.

func TestComputeBloomFilterHitPercentage(t *testing.T) {

network/p2p/gossip/handler.go:18

• The computeBloomFilterHitPercentage function uses zap.Uint64 and zap.Error but go.uber.org/zap is not imported, causing a compile error. Add import "go.uber.org/zap" or switch to the existing logging API.

	safemath "github.com/ava-labs/avalanchego/utils/math"