SG-41387 Add parameter created_at for sg.upload

[jerrycheng9]

Adds an optional created_at parameter to Shotgun.upload() that allows users to specify a custom timestamp for the uploaded Attachment entity.

[codecov]

Codecov Report

❌ Patch coverage is 50.00000% with 4 lines in your changes missing coverage. Please review.
✅ Project coverage is 78.52%. Comparing base (24dfce6) to head (91805a0).

Files with missing lines	Patch %	Lines
shotgun_api3/shotgun.py	50.00%	4 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #444      +/-   ##
==========================================
- Coverage   78.88%   78.52%   -0.36%     
==========================================
  Files           7        7              
  Lines        1842     1849       +7     
==========================================
- Hits         1453     1452       -1     
- Misses        389      397       +8     

Flag	Coverage Δ
Linux	78.52% <50.00%> (-0.14%)	⬇️
Python-3.10	78.47% <50.00%> (-0.14%)	⬇️
Python-3.11	78.47% <50.00%> (-0.14%)	⬇️
Python-3.13	78.47% <50.00%> (-0.36%)	⬇️
Python-3.9	78.46% <50.00%> (-0.14%)	⬇️
Windows	78.61% <50.00%> (-0.14%)	⬇️
macOS	78.47% <50.00%> (-0.41%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.