Merge branch 'modelpar' into gpusf

Both sides kept: modelpar's parallel basis scoring, the second validation
started on a forecast beside the first (write gate, schedule parameter),
the multi-GPU placement and delete-before-rewrite; gpusf's GPU structure
factors, maps and null engine, failure-instead-of-restart, and the merge
engine released before the validation (now just before modelpar's
ValidateAgainstModel call, after the forecast lambda is set up).

Placement: each validation's structure-factor engines (d_min and the
null's) are made on the card of the thread that runs it - the main
thread's for the first validation, card 1 % count for the speculative
second, which pins itself there - so two validations on two cards use
both, as the rigid-body pools do.

One memory rule for both, per card, from total memory, up front: a
validation plans at most half of its card - its structure-factor engines
a quarter together (was half for the d_min engine alone), its rigid-body
engines a quarter (RigidBodyGPUPool) - and the second validation runs
beside the first only where twice the first's plan (rigid-body planned
bytes + the d_min engine, twice it where a null is coming, the null's
engine being no larger) fits half of all cards' memory together (was:
twice the rigid-body plan within a quarter). The card's total is read
once when the engine is made; a CUDA error there fails the validation
like any other.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01SVmAWnzCmRKAXVUCdc4iNi

image_analysis/structure_refinement/ModelStructureFactorsGPU.cpp

@@ -107,7 +107,7 @@ void ModelDensityAtoms(const gemmi::Model &model, const gemmi::DensityCalculator
 
 ModelStructureFactorsGPU::ModelStructureFactorsGPU(int device, const gemmi::Model &model, const gemmi::UnitCell &cell,
                                                    const gemmi::SpaceGroup &sg, double d_min)
-    : device_(device), cell_(cell), sg_(&sg), d_min_(d_min), dc_(Calculator(model, cell, sg, d_min)) {
+    : device_(device), device_total_(ModelStructureFactorsGPUEngine::TotalMemory(device)), cell_(cell), sg_(&sg), d_min_(d_min), dc_(Calculator(model, cell, sg, d_min)) {
     const gemmi::Grid<float> grid = RigidBodyZoneGrid(cell, sg, d_min);   // DensityCalculator's for d_min
     setup_.grid.nu = grid.nu;
     setup_.grid.nv = grid.nv;