Regenerate SDK: optional internal/experimental metrics fields

quotaSnapshots and totalPremiumRequests are now optional+internal;
ShutdownModelMetricRequests.count and .cost are now optional+experimental.
C# fields become nullable and gain [JsonInclude]/[Experimental] attributes.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: SteveSandersonMS

dotnet/src/Generated/SessionEvents.cs

@@ -723,9 +723,25 @@ pub struct ShutdownCodeChanges {
 #[serde(rename_all = "camelCase")]
 pub struct ShutdownModelMetricRequests {
     /// Cumulative cost multiplier for requests to this model
-    pub cost: f64,
+    ///
+    /// <div class="warning">
+    ///
+    /// **Experimental.** This type is part of an experimental wire-protocol surface
+    /// and may change or be removed in future SDK or CLI releases.
+    ///
+    /// </div>
+    #[serde(skip_serializing_if = "Option::is_none")]
+    pub cost: Option<f64>,
     /// Total number of API requests made to this model
-    pub count: i64,
+    ///
+    /// <div class="warning">
+    ///
+    /// **Experimental.** This type is part of an experimental wire-protocol surface
+    /// and may change or be removed in future SDK or CLI releases.
+    ///
+    /// </div>
+    #[serde(skip_serializing_if = "Option::is_none")]
+    pub count: Option<i64>,
 }
 
 /// Schema for the `ShutdownModelMetricTokenDetail` type.
@@ -830,7 +846,9 @@ pub struct SessionShutdownData {
     #[serde(skip_serializing_if = "Option::is_none")]
     pub total_nano_aiu: Option<f64>,
     /// Total number of premium API requests used during the session
-    pub total_premium_requests: f64,
+    #[doc(hidden)]
+    #[serde(skip_serializing_if = "Option::is_none")]
+    pub total_premium_requests: Option<f64>,
 }
 
 /// Session event "session.context_changed". Updated working directory and git context after the change
@@ -1341,6 +1359,7 @@ pub struct AssistantUsageData {
     #[serde(skip_serializing_if = "Option::is_none")]
     pub provider_call_id: Option<String>,
     /// Per-quota resource usage snapshots, keyed by quota identifier
+    #[doc(hidden)]
     #[serde(default)]
     pub quota_snapshots: HashMap<String, AssistantUsageQuotaSnapshot>,
     /// Reasoning effort level used for model calls, if applicable (e.g. "none", "low", "medium", "high", "xhigh", "max")