feat: Response header access, settable timeouts, strict typing

[joramkruijer]

NoREST now requires php >= 8.1, which enabled the adding of strict typing.

This merge also introduces a quite a few changes and improvements:

• Response headers are now accessible via $client->getLastResponseHeaders(), and in the exceptions by calling getResponseHeaders() on the caught exception
• Timeouts for request duration can now be set via $client->setTimeout(60), or directly when constructing a new client: new Client(...)->setTimeout(60). To set a different TLS handshake timeout as well: $client->setTimeout(60, 10). The default timeouts are 30s for the overall request, and 10s for TLS handshakes.
• Unknown content-type in a response will no longer throw an InvalidArgumentException: instead the body is returned as-is, without any decoding being attempted
• Passing invalid request payloads (such as an array with content-type set to text/plain, or a non-array/object payload with content-type application/x-www-form-urlencoded will throw an InvalidArgumentException
• String request payloads are not content-type-encoded: a string passed to post() / put() / patch() is sent as-is regardless of content type. We assume the caller has already encoded strings passed to these functions: simply pass an array or object to have it encoded automatically.
• Content-type is now always guaranteed on the client, even if when constructing NoREST with [] or a headers array that omits it entirely

For development:

• CI code checking has been added, with phpstan (level 9) and phpcs (PSR-12) verified on PHP 8.1 and 8.5. This merge therefore adds dev-dependencies phpstan/phpstan, squizlabs/php_codesniffer and their respective config files.