Make "mode" a Enum

[dad616610]

Summary

This PR introduces an Enum class SimMode to replace raw string representations of simulation modes, providing better type safety and developer experience. Additionally, it identifies and implements a new PhysDomain concept to distinguish between simulation modes and physical domains.

Key Changes

1. Added SimMode Enum:

   class SimMode(Enum):
       HYD = "hydraulics"       # Hydraulic simulation
       HEAT = "heat"             # Thermal simulation
       SEQ = "sequential"        # Sequential coupled simulation
       BIDIR = "bidirectional"   # Bidirectional coupled simulation

   • Replaces raw strings throughout the codebase
   • Provides autocompletion and prevents typos
   • Centralizes mode definitions
2. Added PhysDomain Enum:

   class PhysDomain(Enum):
       HYD = "hydraulics"        # Hydraulic results domain
       HEAT = "heat_transfer"    # Thermal results domain

   • Separates simulation method from physical domain
   • Clarifies previously ambiguous "mode" concept
3. API Improvements:
   • Renamed internal mode parameters to sim_mode for clarity
   • Backward compatibility maintained: Users can still call pipeflow(net, mode="hydraulics")
   • Updated function documentation throughout affected modules
4. Documentation:
   • Updated docstrings for all modified functions
   • Added explanations for new enums in relevant modules

Why Enums?

• IDE Support: Auto-completion and discoverability
• Safety: Eliminates string typos in mode specifications
• Maintainability: All modes defined in single location
• Clarity: Explicit separation of simulation method vs physical domain

Pending Items (Future PRs)

• Updating test cases to use new enums (current tests unchanged to limit scope)

Feedback Requested

Naming Concerns

I'm uncertain if these names are optimal. Please suggest alternatives:

• SimMode → CalcMode?
• PhysDomain → ResultMode?
• Is PhysDomain concept actually needed?

The renaming is trivial, so please don't feel burdened by suggesting your preferences!

Import Concert

Currently enums are imported as:

from pandapipes.enums import SimMode

But would this be more user-friendly?

from pandapipes import SimMode  # Direct top-level import