fix: Add fixes for integration into OL (#95)

* feat: Add functionality for the FirebaseAppCheck call

* fix: Remove unused import

* fix: Add fixes for integration into OL

- remove protected declaration as it will not allow for it to
be used within the OL impl of AppIntegrity
- make getAppCheckToken suspend function to allow for the impl to await
for the reponse from Firebase

app/src/main/java/uk/gov/android/authentication/integrity/appcheck/AppChecker.kt

@@ -6,5 +6,5 @@ import uk.gov.android.authentication.integrity.model.AppCheckToken
 interface AppChecker {
     fun init(context: Context)
 
-    fun getAppCheckToken(): Result<AppCheckToken>
+    suspend fun getAppCheckToken(): Result<AppCheckToken>
 }

app/src/main/java/uk/gov/android/authentication/integrity/usecase/AttestationCaller.kt

@@ -11,6 +11,6 @@ fun interface AttestationCaller {
     data class Response(val jwt: String, val expiresIn: Long)
 
     companion object {
-        protected const val FIREBASE_HEADER = "X-Firebase-AppCheck"
+        const val FIREBASE_HEADER = "X-Firebase-AppCheck"
     }
 }