Feature: allow setting named dimensionless units in a Field

[anshlachamb]

Following the addition of a new Unit ctor on server side, we propose to add the same option on client side:
Field.unit can now be set with a dimensionless (not homogeneous to anything) unit, with a custom name.
Usefull especially for pyAnsys Sound, where lots of "psychoacoustic" units are dimensionless and named.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 84.04%. Comparing base (9f8f63f) to head (03f370c).
Report is 1 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #2295      +/-   ##
==========================================
- Coverage   84.07%   84.04%   -0.04%     
==========================================
  Files          91       91              
  Lines       10506    10514       +8     
==========================================
+ Hits         8833     8836       +3     
- Misses       1673     1678       +5     

[rafacanton]

@anshlachamb Tests are failing because 26.1 server is not up-to-date. They should pass again after today's code update in about 5/6h

[PProfizi]

@rafacanton for some strange reason this is failing only on Docker https://github.com/ansys/pydpf-core/actions/runs/15396696652/job/43319174056?pr=2295#step:17:2768