Fix minimum jumping depth

[lispandfound]

Minimum jumping depth was not being respecting in the source modelling jump point calculator. This fixes it so it can used in Cybershake.

[lispandfound]

@claude review this PR please.

[claude]

Claude finished @lispandfound's task in 2m 35s —— View job

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Review complete ✅

• Gather context (diff, existing review comments)
• Review source_modelling/rupture_propagation.py
• Review source_modelling/sources.py
• Review tests/test_sources.py
• Post findings / summary

Findings: 1 medium, 1 low

1. Medium — source_modelling/rupture_propagation.py:527-530: jump_points_from_rupture_tree passes min_depth straight into sources.closest_points_beneath for every source/parent pair with no clamping. closest_points_beneath raises ValueError if min_depth exceeds the bottom depth of either source. The existing caller in moment.py (connected_components) clamps min_depth per-pair against 0.99 * bottom_m to avoid exactly this; the new code here doesn't, so a Cybershake rupture tree containing a fault/point shallower than the configured min_depth will raise and abort processing of the whole tree instead of gracefully skipping the depth restriction for that pair. No new test exercises this shallow-source case.
2. Low (nit) — source_modelling/rupture_propagation.py:527: elif min_depth: is a truthiness check rather than is not None, so an explicit min_depth=0.0 silently behaves like None. Harmless here since 0 restricts nothing, but worth tightening for clarity.

Everything else (the new Point.top_m/bottom_m properties, the IsSource type widening on closest_points_beneath, and the added test) looks consistent with the existing Plane/Fault conventions.

[AndrewRidden-Harper]

Some minor suggestions for comments

[AndrewRidden-Harper]

Thanks, excellent comments!