Use the selected backend worker (Libp2p vs Litep2p)

[RomarQ]

What does it do?

Context: paritytech/polkadot-sdk#8461

This PR updates Moonbeam’s node startup wiring so the selected P2P backend is actually used. Instead of always building the networking stack with the libp2p worker type, start_node now branches on parachain_config.network.network_backend and instantiates the appropriate backend (Libp2p vs Litep2p). The Litep2p is the default on recent polkadot-sdk versions.

Context

When a node is configured to run with Litep2p, the service should construct the corresponding networking backend. This change ensures Moonbeam respects the configured backend selection and avoids mismatched network worker types.

[coderabbitai]

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✨ Finishing touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Post copyable unit tests in a comment
• Commit unit tests in branch rq/use-the-correct-p2p-backend

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[github-actions]

WASM runtime size check:

Compared to target branch

Moonbase runtime: 2124 KB (no changes) ✅

Moonbeam runtime: 2240 KB (no changes) ✅

Moonriver runtime: 2240 KB (no changes) ✅

Compared to latest release (runtime-4100)

Moonbase runtime: 2124 KB (+188 KB compared to latest release) ⚠️

Moonbeam runtime: 2240 KB (+208 KB compared to latest release) ⚠️

Moonriver runtime: 2240 KB (+208 KB compared to latest release) ⚠️

[github-actions]

Coverage Report

@@                        Coverage Diff                         @@
##           master   rq/use-the-correct-p2p-backend      +/-   ##
==================================================================
- Coverage   76.71%                           76.70%   -0.01%     
  Files         389                              389              
+ Lines       76585                            76595      +10     
==================================================================
  Hits        58745                            58745              
+ Misses      17840                            17850      +10     

Files Changed	Coverage
/node/service/src/lib.rs	48.53% (-0.48%)	🔽

Coverage generated Tue Dec 16 17:33:10 UTC 2025