Allow unknown remote object size

[xinaxu]

This PR handles the edge case when remote data source report object size as unknown (-1)

• The size will not be part of the condition to determine if this file already exists in the database
• Once prepared, the size of the file will be updated to the correct size

Caveats

• Since the size is unknown, it's possible that the files within a job may overflow the sector size
• A warning message is logged so the user is aware

[codecov]

Codecov Report

Attention: Patch coverage is 80.76923% with 10 lines in your changes are missing coverage. Please review.

Project coverage is 74.08%. Comparing base (03cd9d9) to head (5ac733d).

Files	Patch %	Lines
pack/pack.go	70.00%	4 Missing and 2 partials ⚠️
pack/assembler.go	57.14%	2 Missing and 1 partial ⚠️
pack/push/pushfile.go	90.90%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #431      +/-   ##
==========================================
+ Coverage   74.05%   74.08%   +0.03%     
==========================================
  Files         150      150              
  Lines        9954     9980      +26     
==========================================
+ Hits         7371     7394      +23     
- Misses       1824     1826       +2     
- Partials      759      760       +1     

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