Fix async drop glue for Box<T> Fixes rust-lang/rust#143658. This fixes async drop behavior for boxed values so that async drop glue reaches the boxed value’s async destructor in async drop context. The change updates async-drop needs-drop analysis so `Box<T>` is handled specially for async drop by considering the boxed pointee and allocator when deciding whether async drop glue is needed. This PR intentionally does not change the broader AsyncDrop design. It only fixes behavior under the existing `#![feature(async_drop)]` implementation. Reviewer notes: - `async-drop-box-allocator.rs` already covers async-dropping the allocator of a `Box`; this PR adds distinct coverage for the boxed value itself. - Boxed dyn pointees are intentionally not pulled into this fix, preserving existing dynamic async-drop limitations. - The change is isolated to async drop analysis; sync `needs_drop` behavior is unchanged. @rustbot label F-async_drop