Generate Allsky files for HiPS

[astrofrog]

Fixes #515

[codecov]

Codecov Report

❌ Patch coverage is 98.30508% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 88.13%. Comparing base (7a3bf34) to head (f81da86).
⚠️ Report is 4 commits behind head on main.

Files with missing lines	Patch %	Lines
reproject/hips/_allsky.py	98.21%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #608      +/-   ##
==========================================
+ Coverage   87.84%   88.13%   +0.29%     
==========================================
  Files          50       51       +1     
  Lines        2015     2074      +59     
==========================================
+ Hits         1770     1828      +58     
- Misses        245      246       +1     

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