[FSSDK-10544] Refactor Hooks code + tests (#273)

* [FSSDK-10544] hook init subscription code refactor

* [FSSDK-10544] useExperiment code + test refactor

* [FSSDK-10544] useFeature code + test refactor

* [FSSDK-10544] useDecision + useTrackEvent update

* [FSSDK-10544] hook log improvement

* [FSSDK-10544] test comments cleanup

Author: junaed-optimizely