[hvac] [bps] [cfd] Multiple Ifc files

[DaJansenGit]

We need to access multiple IFC files for example to set up the different thermal zones
related to #4

[DaJansenGit]

We have different use cases for multiple IFCs:

High prio

1. Load HVAC IFC and BPS IFC of same building into one bim2sim workflow (high priority)

Low prio

2. Load multiple HVAC or BPS IFC of one building (e.g. every storey as one IFC) (medium priority)
3. Load mulitple BPS IFC of different buildings (e.g. quarter simulations) (lowest priority)

• Use case 3 is a niche which we don't want to address (which also would lead to a lot of changes in the core code)

• Use case 2 could be interesting but we won't address it for now. One could simple use an IFC merge tool and merge the IFCs of the same domain and same tool and building together before starting with bim2sim. We might implement this in the future but @veronikarichter already tried merging with IfcOpenShell and it wasn't not that easy.

• Use case 1 will be addressed by separating the the elements that are passed between the tasks into _bps and _hvac. E.g. load_ifc task can output ifc_bps or ifc_hvac or both of them. This way the adjustments to the core code should be minimal.

[DaJansenGit]

This can be closed for now, as cases 2 and 3 are not important for us at the moment