Fix defining single line interface functions, add support for cat and slicing

[mtfishman]

No description provided.

[codecov]

Codecov Report

Attention: Patch coverage is 9.83607% with 55 lines in your changes missing coverage. Please review.

Project coverage is 40.39%. Comparing base (f30e57d) to head (e8056f1).
Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
src/abstractarrayinterface.jl	0.00%	52 Missing ⚠️
src/traits.jl	0.00%	2 Missing ⚠️
src/abstractinterface.jl	0.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #18      +/-   ##
==========================================
- Coverage   48.77%   40.39%   -8.38%     
==========================================
  Files           9        9              
  Lines         244      302      +58     
==========================================
+ Hits          119      122       +3     
- Misses        125      180      +55     

Flag	Coverage Δ
docs	39.20% <9.83%> (-8.13%)	⬇️

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