fix: Formatting, Cargo.lock, MSRV bump

[loewenheim]

Tidy up a bit.

• MSRV bumped to 1.68.0 because of dependencies.
• Nightly formatting applied.
• Checked in Cargo.lock.

[codecov[bot]]

Codecov Report

Merging #612 (e81d970) into master (88e780c) will decrease coverage by 0.05%. The diff coverage is 25.00%.

:exclamation: Current head e81d970 differs from pull request most recent head 7fec8e7. Consider uploading reports for the commit 7fec8e7 to get more accurate results

@@            Coverage Diff             @@
##           master     #612      +/-   ##
==========================================
- Coverage   73.18%   73.14%   -0.05%     
==========================================
  Files          57       57              
  Lines        6578     6583       +5     
==========================================
+ Hits         4814     4815       +1     
- Misses       1764     1768       +4