port tests from tempdir to tempfile

[decathorpe]

The tempdir crate is unmaintained, was last updated seven years ago, and pulls in really old versions of some of its dependencies.

The tempfile crate is actively maintained and replacing code usages is straightforward.

[decathorpe]

Whoops, looks like I didn't find all places where tempdir is used. Will push a fix.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 86.41%. Comparing base (6bd7086) to head (1bd8fc3).
Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #35      +/-   ##
==========================================
+ Coverage   84.57%   86.41%   +1.83%     
==========================================
  Files           7        7              
  Lines         389      390       +1     
==========================================
+ Hits          329      337       +8     
+ Misses         60       53       -7     

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[al8n]

Thanks!

[decathorpe]

Thanks for merging!