fix: resolve webpack warning for optional date-fns-tz dependency

[martijnrusschen]

Summary

• Uses __non_webpack_require__ to load the optional date-fns-tz module
• This tells webpack to use the native Node.js require at runtime instead of trying to bundle/analyze the module
• Eliminates the "Critical dependency: the request of a dependency is an expression" warning

Background

When date-fns-tz is not installed (it's an optional peer dependency), webpack emits a warning because it can't statically analyze the dynamic require(variable) pattern. By using webpack's special __non_webpack_require__ global, we bypass webpack's bundling analysis while still falling back to regular require in non-webpack environments.

Test plan

• TypeScript type checking passes
• All 1479 tests pass
• Build succeeds and includes the fix in dist output

Fixes #6181

🤖 Generated with Claude Code

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 99.31%. Comparing base (644f2f5) to head (b06237b).

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #6182   +/-   ##
=======================================
  Coverage   99.31%   99.31%           
=======================================
  Files          30       30           
  Lines        3810     3812    +2     
  Branches     1639     1642    +3     
=======================================
+ Hits         3784     3786    +2     
  Misses         25       25           
  Partials        1        1           

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