Add GPT 5.1 to Zed BYOK (#43492)

Release Notes:

- Added support for OpenAI's GPT 5.1 model to BYOK

crates/open_ai/src/open_ai.rs

@@ -85,7 +85,8 @@ pub enum Model {
     FiveMini,
     #[serde(rename = "gpt-5-nano")]
     FiveNano,
-
+    #[serde(rename = "gpt-5.1")]
+    FivePointOne,
     #[serde(rename = "custom")]
     Custom {
         name: String,
@@ -121,6 +122,7 @@ impl Model {
             "gpt-5" => Ok(Self::Five),
             "gpt-5-mini" => Ok(Self::FiveMini),
             "gpt-5-nano" => Ok(Self::FiveNano),
+            "gpt-5.1" => Ok(Self::FivePointOne),
             invalid_id => anyhow::bail!("invalid model id '{invalid_id}'"),
         }
     }
@@ -142,6 +144,7 @@ impl Model {
             Self::Five => "gpt-5",
             Self::FiveMini => "gpt-5-mini",
             Self::FiveNano => "gpt-5-nano",
+            Self::FivePointOne => "gpt-5.1",
             Self::Custom { name, .. } => name,
         }
     }
@@ -163,6 +166,7 @@ impl Model {
             Self::Five => "gpt-5",
             Self::FiveMini => "gpt-5-mini",
             Self::FiveNano => "gpt-5-nano",
+            Self::FivePointOne => "gpt-5.1",
             Self::Custom {
                 name, display_name, ..
             } => display_name.as_ref().unwrap_or(name),
@@ -186,6 +190,7 @@ impl Model {
             Self::Five => 272_000,
             Self::FiveMini => 272_000,
             Self::FiveNano => 272_000,
+            Self::FivePointOne => 400_000,
             Self::Custom { max_tokens, .. } => *max_tokens,
         }
     }
@@ -210,6 +215,7 @@ impl Model {
             Self::Five => Some(128_000),
             Self::FiveMini => Some(128_000),
             Self::FiveNano => Some(128_000),
+            Self::FivePointOne => Some(128_000),
         }
     }
 
@@ -237,6 +243,7 @@ impl Model {
             | Self::FourPointOneNano
             | Self::Five
             | Self::FiveMini
+            | Self::FivePointOne
             | Self::FiveNano => true,
             Self::O1 | Self::O3 | Self::O3Mini | Self::O4Mini | Model::Custom { .. } => false,
         }