test(cells): add S3 transfer e2e coverage [WPB-26729]

[MohamadJaara]

https://wearezeta.atlassian.net/browse/WPB-26729

Goal

Add focused Android E2E coverage for the Kalium Cells S3 transport refactor without exercising the full Shared Drive feature set.

Changes

• provision Cells-enabled teams and conversations in the E2E backend setup
• verify a regular 2 MiB upload and receiver-side download with exact size and SHA-256 checks
• verify the multipart boundary with a 100 MiB + 1 byte file
• cover direct-download cancellation, partial-file cleanup, retry, and final checksum verification
• reuse and extend the existing UI Automator page objects, DocumentsUI flow, and test-support file helpers

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 49.45%. Comparing base (9e50c4b) to head (23f213e).

Additional details and impacted files

@@           Coverage Diff            @@
##           develop    #5048   +/-   ##
========================================
  Coverage    49.45%   49.45%           
========================================
  Files          657      657           
  Lines        23960    23960           
  Branches      3731     3731           
========================================
  Hits         11849    11849           
  Misses       10982    10982           
  Partials      1129     1129           

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