feat: fault topology as a button, with the pair direction from geometry

[lachlangrose]

What

Plan items 6.6 and 6.7.

6.6

• "Calculate topology" in step 3 now runs at once. It uses the fault layer and name field from the data manager. No dialog opens.
• The button is disabled until both are set. The tooltip says why.
• The result and the errors show in a message bar on the step page.
• Removed FaultTopologyWidget, its .ui file and launchers.FAULT_TOPOLOGY. The toolbar action stays and uses the same function.
• The calculation is in loopstructural/main/fault_topology_calc.py. It has no widgets.

6.7

• The map2loop table (Fault1, Fault2) has no direction. Fault1 is only the later fault in the layer. The old code used that order as "abutting fault first".
• Now fault_pair_direction finds the abutting fault from the trace geometry (the fault with an end point on the other trace). Pairs are written as (abutting, other).
• A pair without a direction (crossing, separate, end to end) stays NONE and is listed in the message bar.
• Faults keep the layer order, not alphabetical order.
• A new calculation keeps relationships that already exist. It no longer clears them.

Notes

• Based on feat/faults-only-model.
• The end-point test uses 0.1 % of the trace size. map2loop pairs faults within 500 map units, so a trace that stops far short of another one is left for the user to set.

Tests

• tests/unit/test_fault_topology_calc.py: 15 tests pass.
• tests/qgis/test_fault_topology_button.py: not run. QGIS is not installed on my machine.
• Not tested: the full function with map2loop on real data (for example Hamersley).

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