DM-35458: Always write local datastore files to temporaries

[timj]

This allows for an atomic rename in case something goes wrong
in the file writing.

Checklist

• ran Jenkins
• added a release note for user-visible changes to doc/changes

[codecov]

Codecov Report

Merging #705 (08a51ac) into main (df4b34c) will increase coverage by 0.01%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             main     #705      +/-   ##
==========================================
+ Coverage   84.54%   84.55%   +0.01%     
==========================================
  Files         243      243              
  Lines       31825    31835      +10     
  Branches     5966     5969       +3     
==========================================
+ Hits        26906    26918      +12     
+ Misses       3747     3745       -2     
  Partials     1172     1172              

Impacted Files	Coverage Δ
python/lsst/daf/butler/datastores/fileDatastore.py	81.10% <100.00%> (+0.17%)	⬆️
tests/test_datastore.py	99.48% <100.00%> (+<0.01%)	⬆️

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[ktlim]

Looks OK. Any chance to test the new path? (Maybe start writing a large file, then use inotify to see that the temp file has shown up?)

[timj]

There is not a special path for local files any more. Everything uses a temporary and I can confirm that the log messages are showing that the temporary is in use and is then moved over to the final location.

[ktlim]

But you don't check those log messages in a test case, do you? In this case the side effect of the implementation choice is significant.

[timj]

I don't check the log message. What I can do is add a check that the resources logger is reporting a move transfer for local writes. The only code choice there is is whether a move or copy is happening to the temporary file (and whether the temp file is inside datastore or not).