rimport: Add --check functionality

[samsrabin]

New rimport option --check checks whether file has been published but does not attempt copy.

Resolves #2.

Other changes:

• Always print whether a file can be downloaded from the server.
• If file exists in staging directory but hasn't been linked, print a message with instructions for doing so. (In my next PR, this will be replaced with an actual call of relink.)
• Prints file path and indents messages; useful for tracking messages when rimporting a list of files.

[jedwards4b]

Thanks

[codecov-commenter]

Codecov Report

❌ Patch coverage is 96.19048% with 8 lines in your changes missing coverage. Please review.
✅ Project coverage is 97.76%. Comparing base (ff55606) to head (92cf1a4).
⚠️ Report is 16 commits behind head on main.

Files with missing lines	Patch %	Lines
rimport	89.13%	5 Missing ⚠️
tests/rimport/test_can_file_be_downloaded.py	90.00%	3 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff            @@
##             main      #18    +/-   ##
========================================
  Coverage   97.76%   97.76%            
========================================
  Files          21       22     +1     
  Lines        2010     2195   +185     
========================================
+ Hits         1965     2146   +181     
- Misses         45       49     +4     

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