[Feature Request] Allow for override of tool names with custom client tools

[Davsterl]

Ideally if the client provides a tool, it would be great if we could deterministically overwrite the build in one fully. i.e. if we provide our own apply_patch tool, there would be no conflict as it would replace the in-sdk/CLI one fully.

[MattKotsenas]

I think your request can be implemented like this? --

copilot-sdk/CHANGELOG.md

Lines 314 to 339 in 1587e34

	### Feature: support overriding built-in tools
	Applications can now override built-in tools such as `grep`, `edit_file`, or `read_file`. To do this, register a custom tool with the same name and set the override flag. Without the flag, the runtime will return an error if the name clashes with a built-in. ([#636](https://github.com/github/copilot-sdk/pull/636))
	```ts
	import { defineTool } from "@github/copilot-sdk";
	const session = await client.createSession({
	tools: [defineTool("grep", {
	overridesBuiltInTool: true,
	handler: async (params) => `CUSTOM_GREP_RESULT: ${params.query}`,
	})],
	onPermissionRequest: approveAll,
	});
	```
	```cs
	var grep = AIFunctionFactory.Create(
	([Description("Search query")] string query) => $"CUSTOM_GREP_RESULT: {query}",
	"grep",
	"Custom grep implementation",
	new AIFunctionFactoryOptions
	{
	AdditionalProperties = new ReadOnlyDictionary<string, object?>(
	new Dictionary<string, object?> { ["is_override"] = true })
	});