allow integrand_prototype for oop integral functions

[lxvm]

Previously, IntegralFunction(f, integrand_prototype) would error for oop f and this pr makes it possible to pass an oop f because the integrand_prototype is still useful to infer the return type of f without evaluating it. Integral algorithms often need to have a prototype to have a correct wrapper so this will avoid additional integrand evaluations.

Checklist

• Appropriate tests were added
• Any code changes were done in a way that does not break public API
• All documentation related to code changes were updated
• The new code follows the
  contributor guidelines, in particular the SciML Style Guide and
  COLPRAC.
• Any new documentation only uses public API

Additional context

Add any other context about the problem here.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 26.19%. Comparing base (d45b79a) to head (263f910).
Report is 3 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #636      +/-   ##
==========================================
- Coverage   26.26%   26.19%   -0.07%     
==========================================
  Files          55       55              
  Lines        4283     4279       -4     
==========================================
- Hits         1125     1121       -4     
  Misses       3158     3158              

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