Fixes for complex integrands

[f0uriest]

• Fixes some type mismatches for complex valued integrands
• Adds full testing for integration of complex valued integrands

Resolves #19

[codecov-commenter]

⚠️ Please install the to ensure uploads and comments are reliably processed by Codecov.

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 93.83%. Comparing base (fa14060) to head (b28fb80).
Report is 1 commits behind head on main.

❗ Your organization needs to install the Codecov GitHub app to enable full functionality.

Additional details and impacted files

@@           Coverage Diff           @@
##             main      #20   +/-   ##
=======================================
  Coverage   93.83%   93.83%           
=======================================
  Files           7        7           
  Lines         616      616           
=======================================
  Hits          578      578           
  Misses         38       38           

Files with missing lines	Coverage Δ
quadax/adaptive.py	96.87% <100.00%> (ø)
quadax/fixed_order.py	91.96% <100.00%> (ø)