Handle broken pipe errors on stdout gracefully (#932)

Replace `println!` calls on the results paths with `writeln!` on
`io::stdout()` and propagate the `io::Error` to `main`, where
`ErrorKind::BrokenPipe` is turned into a quiet `exit(0)`. This matches
the conventional behavior of command-line tools when their output pipe
is closed early (e.g. `hyperfine ... | head -n 0`), and fixes panics in
all run-output paths: the per-benchmark header and results, the speed
comparison summary, and `-`-style exports to stdout. The warnings and
"Note" outputs to stderr are converted the same way.


---------

Co-authored-by: Mathjk <Mathjk@users.noreply.github.com>
Co-authored-by: David Peter <mail@david-peter.de>

src/output/mod.rs

@@ -1,3 +1,13 @@
 pub mod format;
 pub mod progress_bar;
 pub mod warnings;
+
+/// Mark console write errors so broken pipes can be handled separately from file errors.
+macro_rules! console_writeln {
+    ($writer:expr $(, $($args:tt)*)?) => {
+        writeln!($writer $(, $($args)*)?)
+            .map_err($crate::error::ConsoleOutputError)
+    };
+}
+
+pub(crate) use console_writeln;