Add missing waitUntil method to FakeInvokedProcess

Problem

The FakeInvokedProcess class was missing the waitUntil method that exists in InvokedProcess, causing test failures when using faked processes.

Solution

Added waitUntil method to both the contract interface and FakeInvokedProcess implementation with comprehensive tests.

Example

Before: This would fail with faked processes

//test 
Process::fake([
    'long-process *' => Process::describe()
          ->output('booting')
          ->output('ready')
          ->iterations(2),
]);

// code
$process = Process::start('long-process');
$result = $process->waitUntil(fn($type, $buffer) => str_contains($buffer, 'ready'));

After: Now works perfectly
// Same code now works with faked processes
$this->assertTrue($result->successful());

Benefits

• Consistent behavior between real and faked processes
• Enables proper testing of asynchronous process workflows
• Fully backward compatible