chore(p2p): Refactor & Test Bootnode Discovery Configs

[refcell]

Summary

The config-building logic is extracted into dedicated discv4_config() and discv5_config() methods on Command to make each concern testable in isolation. Unit tests using rstest are added to assert the discv5 discovery socket port matches --v5-addr and differs from --v4-addr.

[cb-heimdall]

🟡 Heimdall Review Status

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1 Skipped Deployment

Project	Deployment	Actions	Updated (UTC)
base	Ignored	Preview	Apr 30, 2026 8:17pm

[github-actions]

Review Summary

This PR extracts inline discv4/discv5 config-building logic into dedicated methods on Command and adds unit tests. The refactoring itself is clean, but there are correctness issues that should be addressed before merging.

Critical

• discv5 still uses DEFAULT_DISCOVERY_V5_LISTEN_CONFIG — The PR description mentions fixing discv5 port binding, but discv5_config() still passes the hardcoded default listen config to Discv5ConfigBuilder::new() instead of constructing a ListenConfig from self.v5_addr. The actual UDP socket binding is controlled by this inner config, not by the outer Config::builder(self.v5_addr) call. Compare with the full node in node.rs which uses ListenConfig::from_two_sockets(...).

• Test codifies the bug — assert_eq!(config.discovery_socket().port(), DEFAULT_DISCOVERY_V5_PORT) asserts the current broken behavior. Once the listen config is properly wired, this assertion will fail. It should assert command.v5_addr.port() instead.

Minor

• discv4 test is tautological — It constructs the expected value using the same code path as the method under test, then compares 16 individual fields. This can never fail for a logic reason and will break if upstream adds fields. A focused assertion on external_ip_resolver would provide the same signal with less maintenance cost.