chore: Audit and update ProGuard consumer rules

Update consumer-rules.pro with explicit rules:
- Add explicit keep for SdkConfig and SdkConfig.Builder
- Add explicit keep for all model classes (data classes)
- Add clarifying comment about internal collector/helper classes

Internal classes (collector/**, helper/**) are intentionally NOT kept
as they can be safely optimized by R8 - they're not part of the public API.

Verified: Release build with minification succeeds (sample:assembleRelease).

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <[email protected]>

Author: oschwald

device-sdk/consumer-rules.pro

@@ -9,9 +9,16 @@
 # Keep SDK entry points
 -keep class com.maxmind.device.DeviceTracker { *; }
 
+# Keep configuration classes (used via Builder pattern)
+-keep class com.maxmind.device.config.SdkConfig { *; }
+-keep class com.maxmind.device.config.SdkConfig$Builder { *; }
+
 # Kotlin serialization rules for SDK data classes
 -keepattributes InnerClasses
 
+# Keep all model classes (data classes with @Serializable)
+-keep class com.maxmind.device.model.** { *; }
+
 -keepclassmembers class com.maxmind.device.model.** {
     *** Companion;
     kotlinx.serialization.KSerializer serializer(...);
@@ -26,3 +33,7 @@
     static **$* *;
 }
 -keepnames class <2>.<3>
+
+# Note: Internal collector/helper classes (com.maxmind.device.collector.**)
+# are intentionally NOT kept - they can be optimized by R8 as they're not
+# part of the public API.