Transform sync client to execute based on static or dynamic sync strategy

[powerslider]

Summary

Simplify vmsync/client.go to be a thin adapter layer that delegates to either a static or dynamic sync strategy based on configuration.

Current Problems

Problem	Description
Mixed responsibilities	Client handles orchestration, syncer creation, finalization, and engine hooks
Inline branching	Static vs dynamic logic interleaved throughout acceptSyncSummary
Dynamic-only methods	OnEngineX methods are no-ops for static sync but exposed on Client
Long methods	acceptSyncSummary is 65+ lines with multiple concerns
Tight coupling	Finalization logic is embedded in client

NOTE: part of the goal is to prepare the client for the rollout of dynamic state sync support. Check #4646.