Fluid Compat (Forge)

- Ported the API (`api`, `api.event`, `api.compat`), the core service, the Flowing Fluids and Vanilla backends, the config files, the log file and Auto Balanced Compat from the NeoForge 1.21.1 line (2.2.3). Public names and signatures are the same.

Not ported yet: saved per-machine data (Forge 1.20.1 has no attachment system) and the

  config screens.

- The four Flowing Fluids patches, adapted to Forge 1.20.1: the bytecode guards know both the SRG names a real game, uses and the Mojang names of the IDE; the LiquidBlock patch uses a refmap. So, Fluid Compat remains useful if you want the patches to take effect for issues that haven't been fixed in the original mod.

- New start-up probe module (`flowing_fluids_probe`): reports the naming mode, the refmap, and whether Flowing Fluids offers every method and field the core calls.

Platform differences from the NeoForge 1.21.1 line

- `FluidIntakeEvent.Post.getResult()` is `getIntakeResult()` here: Forge's `Event` already declares `getResult()` with

  another return type. Everything else in the public API keeps its name and signature.