feat: Allow cancellation of in-progress Gemini requests and pre-execution checks

- Implements cancellation for Gemini requests while they are actively being processed by the model.
- Extends cancellation support to the  logic within tools. This allows users to cancel operations during the phase where the system is determining if a tool execution requires user confirmation, which can include potentially long-running pre-flight checks or LLM-based corrections.
- Underlying LLM calls for edit corrections (within  and ) and next speaker checks can now also be cancelled.
- Previously, cancellation of the main request was not possible until text started streaming, and pre-execution checks were not cancellable.
- This change leverages the updated SDK's ability to accept an abort token and threads s throughout the request, tool execution, and pre-execution check lifecycle.

Fixes https://github.com/google-gemini/gemini-cli/issues/531

packages/server/src/tools/shell.ts

@@ -98,6 +98,7 @@ export class ShellTool extends BaseTool<ShellToolParams, ToolResult> {
 
   async shouldConfirmExecute(
     params: ShellToolParams,
+    _abortSignal: AbortSignal,
   ): Promise<ToolCallConfirmationDetails | false> {
     if (this.validateToolParams(params)) {
       return false; // skip confirmation, execute call will fail immediately