chore: state for uploads

[achettyiitr]

Description

• Initial efforts to break the uploads file into smaller chunks so that it would be easier to review and understand the code.
• Some feedback around it in here.
• Note: There is no change from the existing code.
• There is a follow-up chore: split state machine #4058

Linear Ticket

• Resolves PIPE-466

Security

• The code changed/added as part of this pull request won't create any security issues with how the software is being used.

[codecov]

Codecov Report

Attention: 1 lines in your changes are missing coverage. Please review.

Comparison is base (6583364) 71.78% compared to head (527b6fd) 71.82%.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #4057      +/-   ##
==========================================
+ Coverage   71.78%   71.82%   +0.04%     
==========================================
  Files         372      373       +1     
  Lines       54984    54982       -2     
==========================================
+ Hits        39472    39493      +21     
+ Misses      13187    13171      -16     
+ Partials     2325     2318       -7     

Files	Coverage Δ
warehouse/router/state.go	100.00% <100.00%> (ø)
warehouse/router/upload.go	70.85% <100.00%> (-0.91%)	⬇️
warehouse/router/identities.go	19.83% <0.00%> (ø)

... and 12 files with indirect coverage changes

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