Component bindgen generates invalid Rust for one-element tuples #1939

host_bindgen! output doesn't compile for a WIT world that uses tuple<T> with one element:

package a:b;
world w { export f: func(x: tuple<u16>) -> tuple<u16>; }

emit_value emits (u16), which Rust reads as u16, not a tuple. The decoder builds the value the same way at hl.rs#L263, and the encoder then fails on .0.

A one-element tuple needs a trailing comma: (u16,).