Fix: concurrent tool execution fails with ProcessDriver due to $this capture and circular references

[vinitkadam03]

Summary

Fixes #893 — concurrent tool execution via Laravel's Concurrency::run() fails because closures capture $this (the handler object), causing SerializableClosure to serialize the entire application container. This also fixes the ->using($this) circular reference issue for class-based invokable tools.

Changes

CallsTools trait — eliminate $this capture in concurrent closures

• Replaced groupToolCallsByConcurrency with resolveToolCalls which resolves each tool exactly once upfront and returns {tool, toolCall} pairs. Unresolvable tools carry the caught exception forward instead of being re-resolved inside the closure.
• Replaced instance method executeToolCall with static method executeResolvedToolCall that receives the pre-resolved Tool directly — no $this, no $tools array in the serialization boundary.
• Concurrent closures are now static fn() calling self::executeResolvedToolCall(), preventing the handler (and its transitive references to the Laravel container) from being serialized.

Tool class — fix circular reference and named argument handling

• using() now detects $fn === $this and skips the assignment, preventing the Tool -> $fn -> Tool circular reference that breaks SerializableClosure.
• handle() auto-detects __invoke() on subclasses when $fn is null, so invokable tool classes work with or without ->using($this).
• handle() unwraps SerializableClosure\Serializers\Native wrappers via getClosure() before invocation, restoring PHP 8 named argument forwarding that Native::__invoke() breaks.

Fixes

• TypeError: Cannot assign SerializableClosure\Serializers\Native to property ... (e.g. Scramble's GeneratorConfig::$uiRoute)
• Error: Cannot modify readonly property ... (e.g. Spatie LaravelData's DataType::$type)
• Named arguments silently broken after ProcessDriver deserialization
• Tool -> $fn -> Tool circular reference with class-based invokable tools using ->using($this)

Test plan

• Existing CallsToolsConcurrentTest — sequential, concurrent, mixed, error handling, grouping
• Existing CallsToolsTest — all tool execution and event generation paths
• Existing ToolTest and ToolErrorHandlingTest — all tool behavior
• Existing ConcurrentToolExecutionTest — concurrent flag behavior
• New: invokable subclass with ->using($this) works without circular reference
• New: invokable subclass works without calling using() at all