Support layers for Augur load

[Zethson]

Fixes #850

• Supports layer for Augur().load()

[codecov-commenter]

Codecov Report

❌ Patch coverage is 82.85714% with 6 lines in your changes missing coverage. Please review.
✅ Project coverage is 72.83%. Comparing base (48953b8) to head (23a3a41).
⚠️ Report is 9 commits behind head on main.

Files with missing lines	Patch %	Lines
pertpy/tools/_augur.py	73.91%	6 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #852      +/-   ##
==========================================
+ Coverage   72.77%   72.83%   +0.06%     
==========================================
  Files          47       48       +1     
  Lines        5524     5548      +24     
==========================================
+ Hits         4020     4041      +21     
- Misses       1504     1507       +3     

Files with missing lines	Coverage Δ
pertpy/tools/core.py	100.00% <100.00%> (ø)
pertpy/tools/_augur.py	88.76% <73.91%> (-0.63%)	⬇️

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