Additional Proguard rules (#44)

Seems like we are stripping something important which is causing a soft
error (loader spins forever).
Something in the rules below seems to resolve it.

See:
- https://square.github.io/retrofit/
- https://square.github.io/okhttp/features/r8_proguard/

Specifically I added these rules:
-
https://github.com/square/retrofit/blob/trunk/retrofit/src/main/resources/META-INF/proguard/retrofit2.pro
-
https://raw.githubusercontent.com/square/okhttp/master/okhttp/src/main/resources/META-INF/proguard/okhttp3.pro
-
https://github.com/square/okio/blob/c90794f83170d770eb247c56ade80c0a6661a5d6/android-test/multidex-config.pro

android/app/proguard-rules.pro

@@ -37,4 +37,73 @@
     kotlinx.serialization.KSerializer serializer(...);
 }
 
+# https://github.com/square/retrofit/blob/trunk/retrofit/src/main/resources/META-INF/proguard/retrofit2.pro
+# Retrofit does reflection on generic parameters. InnerClasses is required to use Signature and
+# EnclosingMethod is required to use InnerClasses.
+-keepattributes Signature, InnerClasses, EnclosingMethod
+
+# Retrofit does reflection on method and parameter annotations.
+-keepattributes RuntimeVisibleAnnotations, RuntimeVisibleParameterAnnotations
+
+# Keep annotation default values (e.g., retrofit2.http.Field.encoded).
+-keepattributes AnnotationDefault
+
+# Retain service method parameters when optimizing.
+-keepclassmembers,allowshrinking,allowobfuscation interface * {
+    @retrofit2.http.* <methods>;
+}
+
+# Ignore annotation used for build tooling.
+-dontwarn org.codehaus.mojo.animal_sniffer.IgnoreJRERequirement
+
+# Ignore JSR 305 annotations for embedding nullability information.
+-dontwarn javax.annotation.**
+
+# Guarded by a NoClassDefFoundError try/catch and only used when on the classpath.
+-dontwarn kotlin.Unit
+
+# Top-level functions that can only be used by Kotlin.
+-dontwarn retrofit2.KotlinExtensions
+-dontwarn retrofit2.KotlinExtensions$*
+
+# With R8 full mode, it sees no subtypes of Retrofit interfaces since they are created with a Proxy
+# and replaces all potential values with null. Explicitly keeping the interfaces prevents this.
+-if interface * { @retrofit2.http.* <methods>; }
+-keep,allowobfuscation interface <1>
+
+# Keep inherited services.
+-if interface * { @retrofit2.http.* <methods>; }
+-keep,allowobfuscation interface * extends <1>
+
+# With R8 full mode generic signatures are stripped for classes that are not
+# kept. Suspend functions are wrapped in continuations where the type argument
+# is used.
+-keep,allowobfuscation,allowshrinking class kotlin.coroutines.Continuation
+
+# R8 full mode strips generic signatures from return types if not kept.
+-if interface * { @retrofit2.http.* public *** *(...); }
+-keep,allowoptimization,allowshrinking,allowobfuscation class <3>
+
+# With R8 full mode generic signatures are stripped for classes that are not kept.
+-keep,allowobfuscation,allowshrinking class retrofit2.Response
+
+# JSR 305 annotations are for embedding nullability information.
+-dontwarn javax.annotation.**
+
+# https://raw.githubusercontent.com/square/okhttp/master/okhttp/src/main/resources/META-INF/proguard/okhttp3.pro
+# A resource is loaded with a relative path so the package of this class must be preserved.
+-keeppackagenames okhttp3.internal.publicsuffix.*
+-adaptresourcefilenames okhttp3/internal/publicsuffix/PublicSuffixDatabase.gz
+
+# Animal Sniffer compileOnly dependency to ensure APIs are compatible with older versions of Java.
+-dontwarn org.codehaus.mojo.animal_sniffer.*
+
+# OkHttp platform used only on JVM and when Conscrypt and other security providers are available.
+-dontwarn okhttp3.internal.platform.**
+-dontwarn org.conscrypt.**
+-dontwarn org.bouncycastle.**
+-dontwarn org.openjsse.**
+
+-keep class okio.** { *; }
+
 -dontobfuscate