Add more std prelude items to crate::prelude

New rustc beta now warns on duplicate imports when one of the
imports is from a wildcard import or the default prelude. Thus, for
simplicity, we need to make our `crate::prelude` mostly identical
to the `std` one, allowing us to always simply use the
`crate::prelude` and let it decide if we need to import anything.

lightning/src/lib.rs

@@ -170,6 +170,9 @@ mod prelude {
 	pub use alloc::borrow::ToOwned;
 	pub use alloc::string::ToString;
 
+	pub use core::convert::{TryFrom, TryInto};
+	pub use core::marker::Sized;
+
 	pub(crate) use crate::util::hash_tables::*;
 }