Prepare v2.7.0 release

[PaulRotmann]

Preparation for release v2.7.0 on 2025-01-24.

[KentarouTakeda]

@clue Are you planning to publish the recent changes, including this pull request, as a new version?

I think #107 in particular is an important change for users. Currently, we are concerned that the following warning message is always displayed when we run tools that use our library on php-8.4 or higher:

Clue\React\Stdio\Stdio::__construct(): Implicitly marking parameter $loop as nullable is deprecated, the explicit nullable type must be used instead

Clue\React\Stdio\Stdio::__construct(): Implicitly marking parameter $input as nullable is deprecated, the explicit nullable type must be used instead

Clue\React\Stdio\Stdio::__construct(): Implicitly marking parameter $output as nullable is deprecated, the explicit nullable type must be used instead

Clue\React\Stdio\Stdio::__construct(): Implicitly marking parameter $readline as nullable is deprecated, the explicit nullable type must be used instead

Clue\React\Stdio\Stdio::createStdin(): Implicitly marking parameter $loop as nullable is deprecated, the explicit nullable type must be used instead

Clue\React\Stdio\Stdio::createStdout(): Implicitly marking parameter $loop as nullable is deprecated, the explicit nullable type must be used instead