perf(sync-service): warm-start parachains from restored database state

[replghost]

Summary

On warm restart, skip the relay chain parachain head fetch and consensus bootstrap when the database already contains known consensus parameters (Aura authorities, slot duration).

Context

PR #3210 fixes the root cause of parachain warm-start hangs (using the initial finalized block from subscribe_all instead of waiting for a new notification). However, even with that fix, cold-path logic still runs on warm start:

1. Fetch parachain head from relay chain via PersistedValidationData runtime call
2. Download ~2 MiB :code from a P2P peer
3. Compile WASM and verify Aura consensus parameters via call proofs

When the database already has valid consensus info (not ChainInformationConsensus::Unknown), steps 1-3 can be skipped entirely.

Proposed approach

• Add restored_chain_information: Option<ValidChainInformation> parameter to start_parachain
• If present and consensus is known, use it directly — skip relay fetch + bootstrap
• If present but consensus is Unknown, still bootstrap (download runtime + verify Aura)
• Verify restored state against the relay chain (confirm parachain head matches or is ahead) rather than blindly trusting the database

Prior work

This was originally part of #3210 but was split out to keep that PR focused on the root cause fix. The implementation existed across these commits:

• fix(light-base): warm-start parachains from database state
• fix(light-base): preserve parachain db state alongside checkpoints

Related

• fix: parachain warm-restart hang #3210 — root cause fix for parachain warm-start hang
• perf(sync-service): skip parachain runtime download on warm start #3214 — skip parachain runtime re-download on warm start (caches runtime in DB)

[replghost]

Closing — this is effectively covered by #3210 + #3214:

• Phase 1 (fetch parachain head from relay): fix: parachain warm-restart hang #3210 fixes the hang and makes this fast (~100ms) by using the initial finalized block from subscribe_all
• Phase 2 (bootstrap runtime): perf(sync-service): skip parachain runtime download on warm start #3214 caches the runtime code in databaseContent and verifies via lightweight Aura call proofs, avoiding the 2 MiB re-download

Skipping Phase 1 entirely (this issue) would save ~100ms but requires trusting the DB for consensus parameters without re-verification. Not worth the trust tradeoff given #3210 makes Phase 1 fast.