fix(event-dispatcher): invoke Closure listeners instead of always failing is_callable

RequireCommand registers an inline listener on InstallerEvents::PRE_OPERATIONS_EXEC
to track dependency_resolution_completed, mirroring PHP's `function () use
(&$dependencyResolutionCompleted) { ... }`. This is Composer's own code, not a
Plugin subscriber, but it went through the shared non-string-callable path, which
checked is_callable() against a hardcoded PhpMixed::Null and always failed,
breaking every `require` that reaches the install step.

Callable::Closure now carries the actual Rc<dyn Fn> instead of being a data-less
placeholder, and is invoked directly (Closures are always callable in PHP). The
ArrayCallable path used by future Plugin subscribers is untouched.

Un-ignoring the two require_command_test cases that cited this bug reveals two
separate, pre-existing issues (a missing ext-requirement warning message, and a
RefCell re-entrancy panic in ConsoleIO::ask_question); their #[ignore] reasons
are updated to describe the real current blocker instead of the now-fixed one.

0 files changed, 0 insertions, 0 deletions