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/error.rs

@@ -3,6 +3,10 @@ use std::num::{self, ParseFloatError, ParseIntError};
 use rust_decimal::Error as DecimalError;
 use thiserror::Error;
 
+#[derive(Debug, Error)]
+#[error(transparent)]
+pub struct ConsoleOutputError(pub std::io::Error);
+
 #[derive(Debug, Error)]
 pub enum ParameterScanError {
     #[error("Error while parsing parameter scan arguments ({0})")]