[wiggle] Don't make generated structs and unions Copy.

Some structs and unions are large enough that making them `Copy` isn't
ideal. wasi-common only needed `Copy` in a few places that were easy to
fix. `SubscriptionClock` is 32 bytes, so it's not a bad a idea to pass
it by reference anyway.

crates/wasi-common/src/snapshots/wasi_snapshot_preview1.rs

@@ -1185,7 +1185,7 @@ impl<'a> WasiSnapshotPreview1 for WasiCtx {
         for subscription in subscriptions {
             match subscription.u {
                 types::SubscriptionU::Clock(clock) => {
-                    let delay = clock::to_relative_ns_delay(clock)?;
+                    let delay = clock::to_relative_ns_delay(&clock)?;
                     log::debug!("poll_oneoff event.u.clock = {:?}", clock);
                     log::debug!("poll_oneoff delay = {:?}ns", delay);
                     let current = poll::ClockEventData {