* Add new syncmode "force-execution-layer"

* Add tests

* Add l2.enginekind flag instead of ForceELSync

* Move l2EngineClientKind to EngineController

* Fix lint

* Rename engine.EngineClientKind to engine.Kind and added engineKind.SupportsPostFinalizationELSync()

* Refactor EL/CL tests in sync_test.go

* Refactor tests in sync_test.go

* Rename engine to ec

* Incorporate enginekind-specific flags into syncConfig, and hide engine kind from the engine controller logic

* Fix tests

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Co-authored-by: protolambda <proto@protolambda.com>