Fix documentation examples in pipe.rs (#11792)

* Fix documentation examples in pipe.rs

Replace todo!() placeholders in documentation examples with actual working code

The examples now show how to properly create random, clocks, and sched instances

needed for WasiCtx::new() function.

* Run pipe documentation examples

Author: jiang1997

crates/wasi-common/src/pipe.rs

@@ -17,13 +17,14 @@ use std::sync::{Arc, RwLock};
 ///
 /// A variety of `From` impls are provided so that common pipe types are easy to create. For example:
 ///
-/// ```no_run
+/// ```rust
 /// use wasi_common::{pipe::ReadPipe, WasiCtx, Table};
 /// let stdin = ReadPipe::from("hello from stdin!");
-/// // Brint these instances from elsewhere (e.g. wasi-cap-std-sync):
-/// let random = todo!();
-/// let clocks = todo!();
-/// let sched = todo!();
+/// // Bring these instances from elsewhere (e.g. wasi-cap-std-sync or wasi-cap-std-tokio):
+/// use wasi_common::sync::{random_ctx, clocks_ctx, sched_ctx};
+/// let random = random_ctx();
+/// let clocks = clocks_ctx();
+/// let sched = sched_ctx();
 /// let table = Table::new();
 /// let mut ctx = WasiCtx::new(random, clocks, sched, table);
 /// ctx.set_stdin(Box::new(stdin.clone()));
@@ -113,13 +114,14 @@ impl<R: Read + Any + Send + Sync> WasiFile for ReadPipe<R> {
 
 /// A virtual pipe write end.
 ///
-/// ```no_run
+/// ```rust
 /// use wasi_common::{pipe::WritePipe, WasiCtx, Table};
 /// let stdout = WritePipe::new_in_memory();
-/// // Brint these instances from elsewhere (e.g. wasi-cap-std-sync):
-/// let random = todo!();
-/// let clocks = todo!();
-/// let sched = todo!();
+/// // Bring these instances from elsewhere (e.g. wasi-cap-std-sync or wasi-cap-std-tokio):
+/// use wasi_common::sync::{random_ctx, clocks_ctx, sched_ctx};
+/// let random = random_ctx();
+/// let clocks = clocks_ctx();
+/// let sched = sched_ctx();
 /// let table = Table::new();
 /// let mut ctx = WasiCtx::new(random, clocks, sched, table);
 /// ctx.set_stdout(Box::new(stdout.clone()));