Add some metrics improvements (#15922)

* Define TCP and QUIC as `InternetProtocol` (no functional change).

* Group types. (No functional changes)

* Rename variables and use range syntax.

* Add `p2pMaxPeers` and `p2pPeerCountDirectionType` metrics

* `p2p_subscribed_topic_peer_total`: Reset to avoid dangling values.

* `validateConfig`:
- Use `Warning` with fields instead of `Warnf`.
- Avoid to both modify in place the input value and return it.

* Add `p2p_minimum_peers_per_subnet` metric.

* `beaconConfig` => `cfg`.

https://github.com/OffchainLabs/prysm/pull/15880#discussion_r2436826215

* Add changelog

---------

Co-authored-by: james-prysm <90280386+james-prysm@users.noreply.github.com>

beacon-chain/sync/initial-sync/service_test.go

@@ -530,12 +530,12 @@ func TestOriginOutsideRetention(t *testing.T) {
 func TestFetchOriginSidecars(t *testing.T) {
 	ctx := t.Context()
 
-	beaconConfig := params.BeaconConfig()
+	cfg := params.BeaconConfig()
 	genesisTime := time.Date(2025, time.August, 10, 0, 0, 0, 0, time.UTC)
-	secondsPerSlot := beaconConfig.SecondsPerSlot
-	slotsPerEpoch := beaconConfig.SlotsPerEpoch
+	secondsPerSlot := cfg.SecondsPerSlot
+	slotsPerEpoch := cfg.SlotsPerEpoch
 	secondsPerEpoch := uint64(slotsPerEpoch.Mul(secondsPerSlot))
-	retentionEpochs := beaconConfig.MinEpochsForDataColumnSidecarsRequest
+	retentionEpochs := cfg.MinEpochsForDataColumnSidecarsRequest
 
 	genesisValidatorRoot := [fieldparams.RootLength]byte{}