Raise an error when the requested font is not found

[HaozheZhang6]

Closes #1920.

Workplane.text(...) / Shape.makeText(...) silently fell back to the default font when the requested font couldn't be found, so a typo'd font name produced text in the wrong font with no indication.

Using Font_FontMgr.FindFont with Font_StrictLevel_Aliases (instead of the default Font_StrictLevel_Any) returns a null handle when the font can't be resolved, so we raise a clear ValueError instead. Aliased/valid fonts still resolve as before. Applied to both font-loading paths (makeText and the free text function), with a test.

[codecov]

Codecov Report

❌ Patch coverage is 66.66667% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 95.76%. Comparing base (f69500e) to head (349f572).

Files with missing lines	Patch %	Lines
cadquery/occ_impl/shapes.py	66.66%	1 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #2062      +/-   ##
==========================================
- Coverage   95.78%   95.76%   -0.02%     
==========================================
  Files          30       30              
  Lines        9427     9431       +4     
  Branches     1404     1406       +2     
==========================================
+ Hits         9030     9032       +2     
- Misses        242      243       +1     
- Partials      155      156       +1     

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