Lock: using tokio processes rather than std ones

Dependencies

• [2] FI3WFMTS Simplifying the locks
• [3] JL4WKA5P Implement the Sanakirja concurrency model in a cross-process way

Change contents

• edit in pijul/src/repository/unix_lock.rs at line 2
  [3.1975]→[3.1975:1994](∅→∅)
  − use std::io::Read;
• replacement in pijul/src/repository/unix_lock.rs at line 24
  [2.227]→[2.227:286](∅→∅)
  − let mut process = std::process::Command::new(&cmd)
  [2.227]

  [2.286]
  + let mut process = tokio::process::Command::new(&cmd)
• edit in pijul/src/repository/unix_lock.rs at line 27
  [2.389]

  [2.389]
  + .stdin(std::process::Stdio::piped())

  + .stderr(std::process::Stdio::piped())
• replacement in pijul/src/repository/unix_lock.rs at line 31
  [2.462]→[2.462:491](∅→∅)
  − s.read(&mut [0u8])?;
  [2.462]

  [2.491]
  + s.read_exact(&mut [0u8]).await?;