Faster startup: ezdxf and vtk imported on use

[kimstik]

import cadquery loaded ezdxf and vtk although most sessions never touch a DXF or a render window. They are now imported by the functions that use them, and a test in a fresh interpreter keeps them out.

Here the import drops from 1.50 to 1.10 seconds - 0.35 for ezdxf with fontTools, 0.15 for vtk - and loads 417 modules instead of 693.

Annotations that name vtk types are forward references now; typing.get_type_hints() on those five functions resolves them once vtk is imported.

[kimstik]

The rest is OCP: registering 321 packages on import, which costs about a second.
Cadquery needs half of them.
Lazy registration in the generator would recover about 0.5 seconds.
Nanobind would go further I guess.

upd:
lazy registration shows 0.16 sec instead of 0.79 on import OCP
requires basic OCP patching CadQuery/OCP#226

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 95.76%. Comparing base (cb26a27) to head (87ca6f5).

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #2097   +/-   ##
=======================================
  Coverage   95.76%   95.76%           
=======================================
  Files          30       30           
  Lines        9584     9587    +3     
  Branches     1437     1437           
=======================================
+ Hits         9178     9181    +3     
  Misses        250      250           
  Partials      156      156           

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