Fix: inject CancellationToken from request context in static commands

[Copilot]

Calling a static command method with a CancellationToken parameter caused a serialization crash (NotSupportedException: Serialization and deserialization of 'System.IntPtr' instances is not supported) because the binding compiler tried to serialize CancellationToken.None as a JSON constant. Since DotVVM bindings have no mechanism to supply a CancellationToken from the client, it should always come from the server's request context.

Changes

• StaticCommandParameterType – Added CurrentCancellationToken = 5 enum value.
• StaticCommandMethodTranslator – In CreateExecutionPlan, detect CancellationToken-typed arguments before the constant/default check and emit CurrentCancellationToken plan entries. These are excluded from the client-side JS args array.
• StaticCommandExecutionPlanSerializer – Serialize CurrentCancellationToken as null (like DefaultValue); deserialize back to a null-arg plan entry.
• StaticCommandExecutor – Resolve CurrentCancellationToken parameters to context.RequestAborted at invocation time.

Example

[AllowStaticCommand]
public static Task<SessionMetadata> GetMetadataAsync(string sessionId, CancellationToken cancellationToken = default)
    => ...;

<!-- Previously threw NotSupportedException; now works correctly -->
<dot:Button Click="{staticCommand: SessionMetadata = realtimeQuery.GetMetadataAsync(SessionId)}" />

The CancellationToken argument is detected at compile time, stripped from the client payload, and re-injected server-side from IDotvvmRequestContext.RequestAborted.

• Fixes Calling async methods with CancellationToken using staticCommand fails on serialization #2099