Adds the side-effect guard discussed in #8149 (comment) (thanks @samsonasik for the catch).

resolveSingleDeclaredClassName() now bails out unless the target file's top level contains only type declarations: class-likes, use statements, statement-form declare, and comments (namespace is checked recursively). Files with top-level function/const definitions or executed statements — e.g. Cli::init(); after the class — keep their require load-bearing, since autoloading replays only the type declarations.

The guard is one extra condition in front of the existing checks, with existing code untouched, so it can only make the rule remove less, never more.

Fixtures:

• skip_class_with_side_effect — class followed by ClassWithInit::init(); (the CodeIgniter-style case)
• skip_class_with_function — class plus a top-level function

Both fail (the require gets removed) without the guard.