chore(p2p/discv5): add deprecation warning and remove unused code #20367

[gzliudan]

Proposed changes

• p2p/discv5: add deprecation warning and remove unused code

• p2p/discv5: remove unused variables

Ref: ethereum#20367

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• build: Changes that affect the build system or external dependencies
• ci: Changes to CI configuration files and scripts
• chore: Changes that don't change source code or tests
• docs: Documentation only changes
• feat: A new feature
• fix: A bug fix
• perf: A code change that improves performance
• refactor: A code change that neither fixes a bug nor adds a feature
• revert: Revert something
• style: Changes that do not affect the meaning of the code
• test: Adding missing tests or correcting existing tests

Impacted Components

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• Consensus
• Account
• Network
• Geth
• Smart Contract
• External components
• Not sure (Please specify below)

Checklist

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• This PR has sufficient test coverage (unit/integration test) OR I have provided reason in the PR description for not having test coverage
• Tested on a private network from the genesis block and monitored the chain operating correctly for multiple epochs.
• Provide an end-to-end test plan in the PR description on how to manually test it on the devnet/testnet.
• Tested the backwards compatibility.
• Tested with XDC nodes running this version co-exist with those running the previous version.
• Relevant documentation has been updated as part of this PR
• N/A

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[Copilot]

Pull request overview

This PR deprecates the p2p/discv5 package (prototype Discovery v5 implementation) and trims unused/legacy code and tests within that package.

Changes:

• Mark p2p/discv5 as deprecated and add a brief README pointing to the upstream Discovery v5 spec.
• Remove unused helpers/fields and leftover commented/debug code in discv5 implementation files.
• Delete unused/disconnected files/tests (e.g., ntp.go, udp_test.go) and test-only helpers no longer referenced.

Reviewed changes

Copilot reviewed 10 out of 10 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
p2p/discv5/udp.go	Removes unused NAT field/import and unused helper methods.
p2p/discv5/udp_test.go	Deletes unused/obsolete UDP tests and related test scaffolding.
p2p/discv5/ticket.go	Removes unused constants/helpers and cleans up commented debug code.
p2p/discv5/table.go	Adds package-level deprecation notice (doc comment).
p2p/discv5/table_test.go	Removes unused test transport/helper code.
p2p/discv5/README	Adds short warning that discv5 is a prototype and links to spec.
p2p/discv5/ntp.go	Removes NTP drift detection code from discv5.
p2p/discv5/node.go	Removes unused node address/pubkey helpers.
p2p/discv5/net.go	Removes unused findnodeQuery field and simplifies shutdown TODO block.
p2p/discv5/net_test.go	Removes unused testnet mining helper and an unused import.

Comments suppressed due to low confidence (1)

p2p/discv5/ticket.go:456

• There is a stray commented closing brace (//}) left inside searchLookupDone, which makes the control flow harder to read and looks like an unfinished edit. It should be removed.

func (s *ticketStore) searchLookupDone(lookup lookupInfo, nodes []*Node, query func(n *Node, topic Topic) []byte) {
	now := mclock.Now()
	for i, n := range nodes {
		if i == 0 || (binary.BigEndian.Uint64(n.sha[:8])^binary.BigEndian.Uint64(lookup.target[:8])) < s.radius[lookup.topic].minRadius {
			if lookup.radiusLookup {
				if lastReq, ok := s.nodeLastReq[n]; !ok || time.Duration(now-lastReq.time) > radiusTC {
					s.nodeLastReq[n] = reqInfo{pingHash: nil, lookup: lookup, time: now}
				}
			}
			if s.canQueryTopic(n, lookup.topic) {
				hash := query(n, lookup.topic)
				if hash != nil {
					s.addTopicQuery(common.BytesToHash(hash), n, lookup)
				}
			}
			//}
		}
	}