Add action hooks to Runtime_Environment_Setup

[ernilambar]

Closes #1269

Adds four do_action() hooks to Runtime_Environment_Setup so integrations can observe or react to the isolated DB / object-cache boundary without patching core logic.

Description

Hook	Fires
wp_plugin_check_before_runtime_setup	Before set_up() mutates state
wp_plugin_check_after_runtime_setup	After set_up() completes (including early-exit path)
wp_plugin_check_before_runtime_cleanup	Before clean_up() mutates state
wp_plugin_check_after_runtime_cleanup	After clean_up() completes (including both early-exit paths)

Each hook receives a single array $context argument with one key: early_exit (bool) — true when the method returned before completing all steps.

Changes

• includes/Checker/Runtime_Environment_Setup.php — do_action() calls added.
• tests/phpunit/tests/Checker/Runtime_Environment_Setup_Tests.php — new test methods.

AI Usage Disclosure

• This PR was created without the help of AI tools
• This PR includes AI-assisted code or content

Used:

• Claude