feat: concurrent tools execution

[vaishnavyogesh]

Description

This PR adds concurrent tool execution, allowing independent tools to run in parallel instead of sequentially. This significantly reduces latency when LLMs execute multiple tools that perform I/O operations like API calls or database queries.

Tools can be marked with ->concurrent() to execute in parallel:

$weatherTool = Tool::as('get_weather')
    ->using(fn ($city) => Http::get("weather.api/{$city}"))
    ->concurrent(); // Runs in parallel

$newsTool = Tool::as('get_news')
    ->using(fn ($topic) => Http::get("news.api/{$topic}"))
    ->concurrent(); // Runs in parallel

When an LLM calls both tools, they execute simultaneously instead of sequentially, reducing total execution time from (the slowest tool's duration).

The implementation uses Laravel's Concurrency driver, preserves event ordering in original tool call order. Works with both streaming and non-streaming responses.

Breaking Changes

None. This feature is fully backward compatible and opt-in. All existing tools continue executing sequentially by default.

[sixlive]

This is sick! Thanks!