feat: Add Closure Handler Support and Custom Input Schema for Tools

[CodeWithKyrian]

What's New

• Closure Handler Support - All MCP element types now accept closures/callables as handlers:

  // Tools
  Mcp::tool(function(float $x, float $y): float {
      return $x * $y;
  })->name('multiply');
  
  // Resources  
  Mcp::resource('system://time', function(): string {
      return now()->toISOString();
  });
  
  // Resource Templates
  Mcp::resourceTemplate('file://{path}', function(string $path): string {
      return file_get_contents($path);
  });
  
  // Prompts
  Mcp::prompt(function(string $topic): array {
      return [['role' => 'user', 'content' => "Write about {$topic}"]];
  });

• Custom Input Schema for Tools - Tools can now define custom JSON schemas for parameter validation:

  Mcp::tool([CalculatorService::class, 'calculate'])
      ->inputSchema([
          'type' => 'object',
          'properties' => [
              'operation' => ['type' => 'string', 'enum' => ['add', 'subtract']],
              'numbers' => ['type' => 'array', 'items' => ['type' => 'number']]
          ],
          'required' => ['operation', 'numbers']
      ]);