feat: add a buffering feature to AdminLog — radicle-ci-broker

Signed-off-by: Lars Wirzenius liw@liw.fi

         filename: Option<PathBuf>,
         file: Option<File>,
         stderr: bool,
         buffer: Option<Vec<u8>>,
     }
     impl AdminLog {

                 filename: None,
                 file: None,
                 stderr: true,
                 buffer: None,
             }
         }
         /// Capture output into a buffer.
         pub fn capture() -> Self {
             Self {
                 filename: None,
                 file: None,
                 stderr: false,
                 buffer: Some(vec![]),
             }
         }
         /// Return current buffer created by `capture`.
         pub fn capture_buffer(&self) -> Option<&[u8]> {
             self.buffer.as_deref()
         }
         /// Create an admin log that writes to a named file.
         pub fn open(filename: &Path) -> Result<Self, LogError> {
             let file = OpenOptions::new()

                 filename: Some(filename.into()),
                 file: Some(file),
                 stderr: false,
                 buffer: None,
             })
         }

                 std::io::stderr()
                     .write_all(msg.as_bytes())
                     .map_err(LogError::WriteLogStderr)?;
             } else if let Some(buf) = self.buffer.as_mut() {
                 buf.extend_from_slice(msg.as_bytes());
             }
             Ok(())
         }