Fix incorrect model name in count token requests to the developer API backend

Author: David Motsonashvili

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

@@ -18,6 +18,7 @@
 package com.google.firebase.ai.common
 
 import com.google.firebase.ai.common.util.fullModelName
+import com.google.firebase.ai.common.util.trimmedModelName
 import com.google.firebase.ai.type.Content
 import com.google.firebase.ai.type.GenerationConfig
 import com.google.firebase.ai.type.ImagenImageFormat
@@ -57,7 +58,7 @@ internal data class CountTokensRequest(
       CountTokensRequest(
         generateContentRequest =
           generateContentRequest.model?.let {
-            generateContentRequest.copy(model = fullModelName(it))
+            generateContentRequest.copy(model = fullModelName(trimmedModelName(it)))
           }
             ?: generateContentRequest
       )

firebase-ai/src/main/kotlin/com/google/firebase/ai/common/util/util.kt

@@ -23,3 +23,5 @@ package com.google.firebase.ai.common.util
  */
 internal fun fullModelName(name: String): String =
   name.takeIf { it.contains("/") } ?: "models/$name"
+
+internal fun trimmedModelName(name: String): String = name.split("/").last()