feat: Support PRE_POST mode

[hpohekar]

closes #3852

Support new PRE_POST launch mode.

>>> pre_post = pyfluent.launch_fluent(ui_mode="gui", mode=pyfluent.FluentMode.PRE_POST) 
>>> from ansys.fluent.core import examples
>>> file_name = examples.download_file("mixing_elbow.cas.h5", "pyfluent/mixing_elbow")
>>> pre_post.settings.file.read_case(file_name=file_name)
Fast-loading "D:\ANSYSDev\vNNN\fluent\fluent25.2\\addons\afd\lib\hdfio.bin"
Done.
Multicore SMT processors detected. Processor affinity set!
>>> pre_post.settings.solution.initialization.hybrid_initialize()     
Hybrid initialization is done.
>>> pre_post.settings.solution.run_calculation.iterate(iter_count=10)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "D:\Repos\pyfluent\src\ansys\fluent\core\solver\flobject.py", line 1797, in __call__
    return self.execute_command(**kwds)
  File "D:\Repos\pyfluent\src\ansys\fluent\core\solver\flobject.py", line 1726, in execute_command
    kwds = _get_new_keywords(self, *args, **kwds)
  File "D:\Repos\pyfluent\src\ansys\fluent\core\solver\flobject.py", line 1610, in _get_new_keywords
    argument_aliases_scm = obj.get_attr("arguments-aliases") or {}
  File "D:\Repos\pyfluent\src\ansys\fluent\core\solver\flobject.py", line 393, in get_attr
    raise InactiveObjectError(self.python_path)
ansys.fluent.core.solver.flobject.InactiveObjectError: '<session>.settings.solution.run_calculation.iterate' is currently inactive.
>>> pre_post.exit()