Fix block parsing regressions and update minimum requirements

[ingeniumed]

Description

Fixes #113, #114, and #115.

Before	After
Custom HTML blocks using the newer role: local definition lose their content.	core/html returns its inner HTML as content; older raw definitions remain supported.
Classic content between blocks can cause a TypeError and fail the entire parse.	Mixed content parses successfully without a misleading unregistered-block warning.
A video with controls turned off returns controls: true.	Boolean HTML attributes reflect presence, so an absent controls attribute returns false.

Raise the minimum requirements to WordPress 6.8 and PHP 8.2. Align the WordPress test dependency and extend CI coverage through PHP 8.5. The existing Symfony 6.4 runtime versions remain in place.

Steps to Test

1. WP_ENV_CORE=WordPress/WordPress#6.8 WP_ENV_PHP_VERSION=8.2 wp-env start
2. composer test
3. composer test-multisite
4. composer phpcs

[alecgeatches]

Tested and these changes work for me. Thanks!