feat: add stepType to largeInt spinbox

[tlambert03]

needed for pyapp-kit/magicgui#572

[codecov]

Codecov Report

Patch coverage: 82.60% and project coverage change: +0.14% 🎉

Comparison is base (0407fdc) 85.89% compared to head (46b1934) 86.03%.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #179      +/-   ##
==========================================
+ Coverage   85.89%   86.03%   +0.14%     
==========================================
  Files          35       35              
  Lines        2702     2722      +20     
==========================================
+ Hits         2321     2342      +21     
+ Misses        381      380       -1     

Files Changed	Coverage Δ
src/superqt/spinbox/_intspin.py	71.01% <82.60%> (+5.76%)	⬆️

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