Add missing optIn declarations to reduce compilation noise

Part of the serialization API we use requires optIn, and without the
correct declarations we get warnings printed when compiling the code.

Author: rlazo

firebase-vertexai/src/main/kotlin/com/google/firebase/vertexai/GenerativeModel.kt

@@ -40,6 +40,7 @@ import com.google.firebase.vertexai.type.content
 import kotlinx.coroutines.flow.Flow
 import kotlinx.coroutines.flow.catch
 import kotlinx.coroutines.flow.map
+import kotlinx.serialization.ExperimentalSerializationApi
 
 /**
  * Represents a multimodal model (like Gemini), capable of generating content based on various input
@@ -199,6 +200,7 @@ internal constructor(
     return countTokens(content { image(prompt) })
   }
 
+  @OptIn(ExperimentalSerializationApi::class)
   private fun constructRequest(vararg prompt: Content) =
     GenerateContentRequest(
       modelName,

firebase-vertexai/src/main/kotlin/com/google/firebase/vertexai/common/Request.kt

@@ -13,7 +13,7 @@
  * See the License for the specific language governing permissions and
  * limitations under the License.
  */
-
+@file:OptIn(ExperimentalSerializationApi::class)
 package com.google.firebase.vertexai.common
 
 import com.google.firebase.vertexai.common.util.fullModelName
@@ -24,6 +24,7 @@ import com.google.firebase.vertexai.type.PublicPreviewAPI
 import com.google.firebase.vertexai.type.SafetySetting
 import com.google.firebase.vertexai.type.Tool
 import com.google.firebase.vertexai.type.ToolConfig
+import kotlinx.serialization.ExperimentalSerializationApi
 import kotlinx.serialization.SerialName
 import kotlinx.serialization.Serializable
 
@@ -49,14 +50,6 @@ internal data class CountTokensRequest(
   @SerialName("system_instruction") val systemInstruction: Content.Internal? = null,
 ) : Request {
   companion object {
-    fun forGenAI(generateContentRequest: GenerateContentRequest) =
-      CountTokensRequest(
-        generateContentRequest =
-          generateContentRequest.model?.let {
-            generateContentRequest.copy(model = fullModelName(it))
-          }
-            ?: generateContentRequest
-      )
 
     fun forVertexAI(generateContentRequest: GenerateContentRequest) =
       CountTokensRequest(

firebase-vertexai/src/main/kotlin/com/google/firebase/vertexai/type/Candidate.kt

@@ -14,6 +14,8 @@
  * limitations under the License.
  */
 
+@file:OptIn(ExperimentalSerializationApi::class)
+
 package com.google.firebase.vertexai.type
 
 import com.google.firebase.vertexai.common.util.FirstOrdinalSerializer

firebase-vertexai/src/main/kotlin/com/google/firebase/vertexai/type/Content.kt

@@ -80,6 +80,7 @@ constructor(public val role: String? = "user", public val parts: List<Part>) {
     public fun build(): Content = Content(role, parts)
   }
 
+  @OptIn(ExperimentalSerializationApi::class)
   internal fun toInternal() = Internal(this.role ?: "user", this.parts.map { it.toInternal() })
 
   @ExperimentalSerializationApi

firebase-vertexai/src/test/java/com/google/firebase/vertexai/GenerativeModelTesting.kt

@@ -40,6 +40,7 @@ import io.ktor.http.content.TextContent
 import io.ktor.http.headersOf
 import kotlin.time.Duration.Companion.seconds
 import kotlinx.coroutines.withTimeout
+import kotlinx.serialization.ExperimentalSerializationApi
 import kotlinx.serialization.encodeToString
 import org.junit.Test
 
@@ -127,6 +128,7 @@ internal class GenerativeModelTesting {
     exception.message shouldContain "location"
   }
 
+  @OptIn(ExperimentalSerializationApi::class)
   private fun generateContentResponseAsJsonString(text: String): String {
     return JSON.encodeToString(
       GenerateContentResponse.Internal(

firebase-vertexai/src/test/java/com/google/firebase/vertexai/common/APIControllerTests.kt

@@ -46,6 +46,7 @@ import kotlin.time.Duration.Companion.milliseconds
 import kotlin.time.Duration.Companion.seconds
 import kotlinx.coroutines.delay
 import kotlinx.coroutines.withTimeout
+import kotlinx.serialization.ExperimentalSerializationApi
 import kotlinx.serialization.encodeToString
 import kotlinx.serialization.json.JsonObject
 import org.junit.Test
@@ -84,6 +85,7 @@ internal class APIControllerTests {
     }
 }
 
+@OptIn(ExperimentalSerializationApi::class)
 internal class RequestFormatTests {
   @Test
   fun `using default endpoint`() = doBlocking {

firebase-vertexai/src/test/java/com/google/firebase/vertexai/common/StreamingSnapshotTests.kt

@@ -30,8 +30,10 @@ import kotlin.time.Duration.Companion.seconds
 import kotlinx.coroutines.flow.collect
 import kotlinx.coroutines.flow.toList
 import kotlinx.coroutines.withTimeout
+import kotlinx.serialization.ExperimentalSerializationApi
 import org.junit.Test
 
+@OptIn(ExperimentalSerializationApi::class)
 internal class StreamingSnapshotTests {
   private val testTimeout = 5.seconds