* Remove `SIMULATED_STORE` flag
* Remove unnecessary test (now that the compiler flag does not exist anymore)
* remove `.testStore` enum case from `Store`
Will be added in the future once the test store is released publicly
* Rename variables for internal consistency
* POST Receipt: send `test_$PURDCHASETIME_$UUID` for `fetch_token` field for simulated store purchases
* add unit tests
* add unit test for POST receipt when purchasing in the Simulated Store
* PR comment
* Rename Test Store to Simulated Store only internally
* fix lint
* fix test under `SIMULATED_STORE` compiler flag
* fix test compilation
* Add name clarification to `APIKeyValidationResult.simulatedStore` enum case
* Fix public-facing strings
* Improve comment
* improve comment