Move to a generic GlobalLazy<T> (#2851)

* Expose a generic lazy type

* Switch to generic lazy globals

* simplify global lazy context a bit

* rename LazyGlobal to Global

* use Memo::global in more examples

* Fix soundness issue with deref_impl. It relies on the size of self, so it cannot be safe

* add a comment about safety

* Make clippy happy

* fix formatting

* Restore changes to signal impl

* Add helper methods for global signal and global memo to make getting the inner value easier

packages/hooks/src/use_future.rs

@@ -189,6 +189,6 @@ impl Deref for UseFuture {
     type Target = dyn Fn() -> UseFutureState;
 
     fn deref(&self) -> &Self::Target {
-        Readable::deref_impl(self)
+        unsafe { Readable::deref_impl(self) }
     }
 }