Fix intent in get_initial_step

[ivan-pi]

The opt object has const in the C interface: https://github.com/stevengj/nlopt/blob/ad8ba827fc2bafb103e01736f261a1faa7ea875e/src/api/nlopt.h#L292

[codecov]

Codecov Report

Merging #17 (92911cf) into main (7e26398) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##             main      #17   +/-   ##
=======================================
  Coverage   29.48%   29.48%           
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  Files           8        8           
  Lines         563      563           
  Branches      153      153           
=======================================
  Hits          166      166           
  Misses        274      274           
  Partials      123      123           

Impacted Files	Coverage Δ
src/nlopt_wrap.f90	12.85% <ø> (ø)

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[ivan-pi]

I just noticed that several other getters also have attribute intent(inout). Is that a conscious decision?

[awvwgk]

I think I used intent(inout) everywhere. One option for error handling was to have an internal state, which saves the last error, in this case the instance could always be changed. But that is not how I implemented things in the end, so we can switch to intent(in) where possible.