fix: Don't default to dev mode for production builds when using vite-node loader

[aklinker1]

This closes #873.

This does cause vite-node's dev server to run in different modes when doing wxt vs wxt build, but I don't expect that to cause any problems.

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[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 82.60%. Comparing base (fb22bea) to head (cb1fa2e).

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #877      +/-   ##
==========================================
+ Coverage   82.46%   82.60%   +0.14%     
==========================================
  Files         124      124              
  Lines        6512     6513       +1     
  Branches     1094     1087       -7     
==========================================
+ Hits         5370     5380      +10     
+ Misses       1128     1119       -9     
  Partials       14       14              

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