refactor: derive Clone on iox_time::SystemProvider

This lets us use a SystemProvider without wrapping it in an Arc to
satisfy a Clone bound.

There's no reason to be wrapping this in an Arc and maintaining
refcounts for a stateless trait impl struct that doesn't have any data
to reference count or drop.

iox_time/src/lib.rs

@@ -213,7 +213,7 @@ pub trait TimeProvider: std::fmt::Debug + Send + Sync + 'static {
 }
 
 /// A [`TimeProvider`] that uses [`Utc::now`] as a clock source
-#[derive(Debug, Default)]
+#[derive(Debug, Default, Clone)]
 pub struct SystemProvider {}
 
 impl SystemProvider {