Allow Anthropic custom models to override temperature (#18160)

Release Notes:

- Allow Anthropic custom models to override "temperature"

This also centralized the defaulting of "temperature" to be inside of
each model's `into_x` call instead of being sprinkled around the code.

crates/anthropic/src/anthropic.rs

@@ -49,6 +49,7 @@ pub enum Model {
         /// Indicates whether this custom model supports caching.
         cache_configuration: Option<AnthropicModelCacheConfiguration>,
         max_output_tokens: Option<u32>,
+        default_temperature: Option<f32>,
     },
 }
 
@@ -124,6 +125,19 @@ impl Model {
         }
     }
 
+    pub fn default_temperature(&self) -> f32 {
+        match self {
+            Self::Claude3_5Sonnet
+            | Self::Claude3Opus
+            | Self::Claude3Sonnet
+            | Self::Claude3Haiku => 1.0,
+            Self::Custom {
+                default_temperature,
+                ..
+            } => default_temperature.unwrap_or(1.0),
+        }
+    }
+
     pub fn tool_model_id(&self) -> &str {
         if let Self::Custom {
             tool_override: Some(tool_override),