Add DXF as an exportable 2D format

[alteous]

There is no corresponding import 2D format yet. This is intended only as an export format from the engine. Conversions to/from DXF are not supported yet.

[alteous]

Ideally OutputFormat would be renamed as OutputFormat3d but that would break everything. Perhaps we could add an alias for compatibility?

[codecov]

Codecov Report

Attention: Patch coverage is 0% with 55 lines in your changes missing coverage. Please review.

Please upload report for BASE (main@eda2f19). Learn more about missing BASE report.

Files with missing lines	Patch %	Lines
modeling-cmds/src/format/mod.rs	0.00%	40 Missing ⚠️
modeling-cmds/src/convert_client_crate.rs	0.00%	8 Missing ⚠️
modeling-cmds/src/format/dxf.rs	0.00%	3 Missing ⚠️
modeling-cmds/src/def_enum.rs	0.00%	2 Missing ⚠️
modeling-cmds/src/shared.rs	0.00%	2 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #762   +/-   ##
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  Coverage        ?   24.91%           
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  Files           ?       36           
  Lines           ?     2131           
  Branches        ?        0           
=======================================
  Hits            ?      531           
  Misses          ?     1600           
  Partials        ?        0           

Flag	Coverage Δ
unittests	24.91% <0.00%> (?)

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