Fix: Correct nullability for FunctionCallPartDto.args

Resolves a compilation type mismatch error in PhotoReasoningMappers.kt related to the 'args' field of FunctionCallPart and FunctionCallPartDto.

The `args` field in `FunctionCallPartDto` has been changed from `Map<String, String>?` to `Map<String, String?>?`. This allows the values within the map to be null, aligning with the inferred type from the SDK's `FunctionCallPart.args` and the type expected by its constructor.

This change ensures that the direct assignment `args = this.args` in both `toDto` and `toSdk` mapping functions for `FunctionCallPart` is now type-correct, fixing the build failure.

Author: google-labs-jules[bot]

app/src/main/kotlin/com/google/ai/sample/feature/multimodal/dtos/PhotoReasoningDtos.kt

@@ -51,7 +51,7 @@ data class BlobPartDto(
 @SerialName("functionCall")
 data class FunctionCallPartDto(
     val name: String,
-    val args: Map<String, String>? // Map<String, String> is serializable by default
+    val args: Map<String, String?>? // Changed to allow nullable String values in the map
 ) : PartDto
 
 @Serializable