fix: add Send trait to stderr & stdout of ExecResult (#809)

Solves:
#808

This has been locally tested and confirmed to solve the issue. It passes
`cargo t` locally.

Author: amab8901

testcontainers/src/core/containers/async_container/exec.rs

@@ -23,12 +23,12 @@ impl ExecResult {
     }
 
     /// Returns an asynchronous reader for stdout. It follows log stream until the command exits.
-    pub fn stdout<'b>(&'b mut self) -> Pin<Box<dyn AsyncBufRead + 'b>> {
+    pub fn stdout<'b>(&'b mut self) -> Pin<Box<dyn AsyncBufRead + Send + 'b>> {
         Box::pin(tokio_util::io::StreamReader::new(&mut self.stdout))
     }
 
     /// Returns an asynchronous reader for stderr. It follows log stream until the command exits.
-    pub fn stderr<'b>(&'b mut self) -> Pin<Box<dyn AsyncBufRead + 'b>> {
+    pub fn stderr<'b>(&'b mut self) -> Pin<Box<dyn AsyncBufRead + Send + 'b>> {
         Box::pin(tokio_util::io::StreamReader::new(&mut self.stderr))
     }
 

testcontainers/src/core/containers/sync_container/exec.rs

@@ -19,15 +19,15 @@ impl SyncExecResult {
     }
 
     /// Returns an asynchronous reader for stdout.
-    pub fn stdout<'b>(&'b mut self) -> Box<dyn BufRead + 'b> {
+    pub fn stdout<'b>(&'b mut self) -> Box<dyn BufRead + Send + 'b> {
         Box::new(sync_reader::SyncReadBridge::new(
             self.inner.stdout(),
             self.runtime.clone(),
         ))
     }
 
     /// Returns an asynchronous reader for stderr.
-    pub fn stderr<'b>(&'b mut self) -> Box<dyn BufRead + 'b> {
+    pub fn stderr<'b>(&'b mut self) -> Box<dyn BufRead + Send + 'b> {
         Box::new(sync_reader::SyncReadBridge::new(
             self.inner.stderr(),
             self.runtime.clone(),