Feat: Add support for client-executed tools

[vinitkadam03]

Description

Summary

This PR introduces support for client-executed tools (also referred to as "deferred tools") - tools that are defined without a handler function and are intended to be executed by the client/caller rather than by Prism.

Motivation

Client-executed tools enable scenarios where tool execution must happen on the client side, such as:

• UI interactions requiring client-side execution
• Any tool where the server should not (or cannot) execute the logic

Changes

Core Implementation

src/Tool.php

• Added isClientExecuted() method that returns true when no handler function is defined ($this->fn === null)

public function isClientExecuted(): bool
{
    return $this->fn === null;
}

src/Concerns/CallsTools.php

• Modified callTools() to filter out client-executed tools from execution
• Added hasDeferredTools() method to check if any tool calls are for client-executed tools

Behavior:

• Client-executed tools are skipped during tool execution
• Server-executed tools in the same request are still executed normally
• When client-executed tools are detected, execution stops and control is returned to the caller
• The LLM is not called for the next turn, allowing the client to execute the tool and continue the conversation
• Response/stream ends with FinishReason::ToolCalls

Usage Example

use Prism\Prism\Facades\Prism;
use Prism\Prism\Facades\Tool;

// Define a client-executed tool (no `using()` call)
$clientTool = Tool::as('client_tool')
    ->for('A tool that executes on the client')
    ->withStringParameter('input', 'Input parameter');
    // Note: No ->using() call!

Breaking Changes

None. This is a backward-compatible addition. Existing tools with handlers continue to work exactly as before.