Fix incorrect top-level imports causing artificial circular-import constraints

[seanpearsonuk]

Hadn't noticed this previously. 👎

Originally posted by @seanpearsonuk in #4656

Body:

Several modules import PyFluent internals via the top-level package instead of their actual module paths, which creates unnecessary circular-import constraints.

Examples:

• logger.py does:

  from ansys.fluent.core import config

  This re-enters __init__.py and forces the current “config must be imported before logging” ordering.
  It should import directly:

  from ansys.fluent.core.module_config import config

• In other places, methods do:

  import ansys.fluent.core as pyfluent
  something = pyfluent.config.get_whatever()

  This is again using the top-level package as a proxy for internal modules, which tightly couples everything to __init__.py execution order.

Proposed fix:

• Replace all top-level imports (from ansys.fluent.core import X or import ansys.fluent.core as pyfluent) with direct module imports (from ansys.fluent.core.module_config import config, etc.).
• This eliminates the circular-import dance and removes the artificial ordering rule in __init__.py.

[prmukherj]

Mark this as well: #4656 (comment)