Emit menu interface defaults inline in exported code

[BradyAJohnston]

The exporter wrote menu interface defaults as a trailing var.default_value = ... after the tree body. The builder already defers menu defaults to context exit, so they can be passed at creation: tree.inputs.menu("Menu", "Tetrahedral").

Removes the exporter's deferral plumbing and bumps to 520.34.1.

[codecov]

Codecov Report

❌ Patch coverage is 80.00000% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 98.30%. Comparing base (1d5aed1) to head (6c37abd).

Files with missing lines	Patch %	Lines
src/nodebpy/export/codegen.py	80.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #250      +/-   ##
==========================================
- Coverage   98.30%   98.30%   -0.01%     
==========================================
  Files         101      101              
  Lines       30565    30556       -9     
==========================================
- Hits        30048    30039       -9     
  Misses        517      517              

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