Step 3: Sync score update from probes

[Tomelia1999]

Summary

Probes now contribute to the sync score in addition to availability and latency. AppendProbeRelayData gains a syncBlock uint64 parameter; the sync-scoring path mirrors appendRelayData with probe weight (0.25). The new write path to latestSyncData.Block is protected by Step 2's majorityBaseline guard.

Docs

• Detailed proposal: protocol/rpcconsumer/docs/probing/improvements-proposals/syncBlock-penalty.md
• Progress: protocol/rpcconsumer/docs/probing/improvements-proposals/fixes-progress.md (Step 3)

Test plan

• `go test ./protocol/... ./ecosystem/cache/...` green
• New unit tests in `provider_optimizer_test.go` covering sync-block update, regression detection, syncBlock=0 skip, relay-vs-probe weight comparison

Stacked PR

Depends on #2297 (Steps 1+2). Targets `epochFloor-implementation`.

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