Support for integer/binary vars for MOSEK

[ulfworsoe]

Add support for integer/binary vars for MOSEK solver direct mode.

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 0% with 8 lines in your changes are missing coverage. Please review.

Project coverage is 80.91%. Comparing base (b298e3c) to head (ac58def).

Files	Patch %	Lines
linopy/io.py	0.00%	7 Missing :warning:
linopy/solvers.py	0.00%	1 Missing :warning:

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #275      +/-   ##
==========================================
- Coverage   88.91%   80.91%   -8.01%     
==========================================
  Files          15       15              
  Lines        3682     3688       +6     
  Branches      866      870       +4     
==========================================
- Hits         3274     2984     -290     
- Misses        283      594     +311     
+ Partials      125      110      -15     

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