Add preextrusion_ops and cavity etch regression test

[hughcars]

Summary

• Adds preextrusion_ops keyword to SolidModelTarget for operations that must
  run before layer extrusions (e.g., 2D metal patterning that would otherwise be
  destroyed by OCC's recursive deletion when 3D extrusions are consumed by boolean ops)
• Adds a cavity etch solidmodel test exercising substrate/cavity/vacuum domain
  decomposition with overlapping 2D surfaces extruded to different depths

The postrender pipeline order is now:
preextrusion_ops → extrusion_ops → postrender_ops → intersection_ops

Cavity etch test

The new test creates a geometry with three concentric rectangles (cavity, metal_negative,
chip_area/simulated_area), extrudes them into volumes at different heights, performs boolean
domain decomposition (substrate = chip - cavity, vacuum = sim - substrate), then verifies
physical groups exist and 3D meshing succeeds.

This test currently requires a patched Gmsh 4.15.0 to pass. Stock 4.15.0 produces
PLC mesh errors due to two bugs in booleanOperator's preserve-numbering path:

1. Ascending-dim unbind order leaves stale face bindings when parent volumes block _unbind
2. Entity map uses stale integer tags instead of shape identity for unmodified entities

A patch for GModelIO_OCC.cpp has been prepared against Gmsh master and will be submitted
upstream. Once a patched gmsh_jll is available (via Yggdrasil), this test will pass in CI.

Test plan

• Full test suite passes with patched Gmsh 4.15.0 (5425 pass, 1 Aqua stale deps)
• Full test suite passes with patched Gmsh 5.0.0 master
• Cavity etch test fails on stock Gmsh 4.15.0 (PLC Error crash) — confirms the test catches the bug
• preextrusion_ops=[] default is backward-compatible — no existing behavior changes