[handle-later] do not decode envSecret every time when getting feature flag

[deleteLater]

ffc-go-sdk/ffc/ffc_client.go

Lines 406 to 408 in f0961dd

	func (c *Client) getFlagInternal(featureFlagKey string) data.FeatureFlag {
	flagId := data.NewFeatureFlagIdByEnvSecret(c.EnvSecret, featureFlagKey).GetFeatureFlagId()
	item := c.dataStorage.Get(data.FeaturesCat, flagId)

every time we get feature flag from dataStorage, we have to decode the envSecret, which is unreasonable.