Add _sym_uplo to skip validation

[jishnub]

In all the places where sym_uplo is used within this package, it is used in a context where uplo in ('U', 'L'), so the error path is never taken. We may therefore remove the error branch from the function and improve the effects inference.

julia> Base.infer_effects(LinearAlgebra.sym_uplo, (Char,))
(+c,+e,!n,+t,+s,+m,+u,+o,+r)

julia> Base.infer_effects(LinearAlgebra.sym_uplo_unsafe, (Char,))
(+c,+e,+n,+t,+s,+m,+u,+o,+r)

I've not removed the sym_uplo function, since this is used by some packages in the ecosystem (e.g., JuMP).

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 93.90%. Comparing base (98723df) to head (eb5a514).
⚠️ Report is 1 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #1441   +/-   ##
=======================================
  Coverage   93.89%   93.90%           
=======================================
  Files          34       34           
  Lines       15920    15925    +5     
=======================================
+ Hits        14948    14954    +6     
+ Misses        972      971    -1     

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[dkarrasch]

What about making this a one-line function?

[dkarrasch]

Can you please add tests that check the three possible outcomes of the previous sym_uplo function to make sure (a) it's covered, (b) it doesn't change behavior, and finally (c) doesn't get removed by accident.

[jishnub]

@dkarrasch good to merge?