Improve DAQP Prox

[Copilot]

LP iteration counts differed between the current branch and v0.8.1 when run through the CMake benchmark (-DBENCHMARK=ON). The root cause was a combination of a broken benchmark comparison path and an off-by-one in the proximal stagnation loop.

Changes

src/api.c — restore n_prox = n for LPs

The previous session removed this, which routed LPs to daqp_ldp directly and broke LP solving. Restored: setup_daqp_ldp must set work->n_prox = work->n for LPs so daqp_solve routes them to daqp_prox.

src/daqp_prox.c — fix cycle-counter increment (LP stagnation)

Pre-increment (++cycle_counter) caused stagnation to fire one outer step earlier than v0.8.1 (11 vs 12 consecutive non-improving steps). Changed to post-increment to match v0.8.1 exactly.

// before (fires after 11 stagnation steps)
if(++cycle_counter > work->settings->cycle_tol)

// after (matches v0.8.1: fires after 12 stagnation steps)
if(cycle_counter++ > work->settings->cycle_tol)

interfaces/daqp-julia/src/api.jl — restore eps_prox=1 for LP setup

Required for pre-v0.9 C libraries that dispatch via eps_prox != 0 rather than n_prox. Without this, old libs route LPs to daqp_ldp.

interfaces/daqp-julia/test/benchmark.jl — fair old-lib comparison

The workspace struct grew by 16 bytes (prox_mask + n_prox) between v0.8.1 and current, shifting the settings pointer from offset 208 → 224. When the benchmark swaps in the v0.8.1 .so, Julia's settings() reads from the wrong offset (gets NULL) and silently fails to set eps_prox=1 — so the old lib takes the daqp_ldp path (few iterations) while the current lib takes daqp_prox (many iterations), making the comparison unfair.

Fix: benchmark_lp now uses the old-style quadprog(QPj; settings=...) API with an explicit DAQPSettings struct where eps_prox=1. This passes settings directly to daqp_quadprog by pointer, bypassing the workspace struct entirely and working correctly with both old and new library ABIs.

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