Show aggregate P2P bandwidth on dashboard

[tdenisenko]

Summary

This PR replaces the dashboard's execution-only P2P download tile with an aggregate P2P bandwidth metric that shows both download and upload Mbps.

The dashboard value now aggregates execution-layer and consensus-layer payload throughput so the main UI reflects the data LogEx is processing across:

• execution forward sync
• execution historical sync
• consensus light-client RPC and gossip

What Changed

• Added upload fields to ExecutionNetworkStatus and download/upload fields to ConsensusNetworkStatus.
• Added consensus-layer rolling payload bandwidth accounting for:
  • inbound/outbound RPC requests and responses
  • consensus gossip payload downloads
• Added execution-layer upload accounting for:
  • outbound header/body/receipt request payloads
  • headers, bodies, transactions, and receipts served from ServeCacheProvider
• Included execution header responses in the execution download payload rate.
• Renamed the dashboard label from P2P download to P2P bandwidth.
• Updated the main dashboard tile to display ↓ download Mbps / ↑ upload Mbps.
• Updated advanced metrics to show aggregate bandwidth plus cumulative down/up payload totals.
• Updated /status test fixtures and assertions for the new fields.
• Added serve-cache coverage for upload snapshot accounting.
• Updated ROADMAP.md for the bandwidth dashboard task.

Notes

The metric is intentionally application payload throughput, not OS network-interface throughput. This avoids counting unrelated host traffic and gives a better LogEx-specific view, but it does not include encrypted transport framing, TCP/IP overhead, or non-LogEx traffic.

Validation

• cargo fmt --check
• cargo check -p logex-types -p logex-cl -p logex-sync -p logex-server
• cargo test -p logex-server
• cargo test -p logex-sync p2p::serve_cache
• cargo test -p logex-cl network::tests
• cargo clippy -p logex-types -p logex-cl -p logex-sync -p logex-server -- -D warnings