fix #9030: box mode objectives are now optimized independently

In box mode (opt.priority=box), each objective should be optimized
independently. Previously, box() called geometric_opt() which optimizes
all objectives together using a shared disjunction of bounds. This caused
adding/removing an objective to change the optimal values of other
objectives.

Fix: Rewrite box() to optimize each objective in its own push/pop scope
using geometric_lex, ensuring complete isolation between objectives.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

src/test/main.cpp

@@ -78,6 +78,7 @@
     X(max_rev) \
     X(scaled_min) \
     X(box_mod_opt) \
+    X(box_independent) \
     X(deep_api_bugs) \
     X(api_algebraic) \
     X(api_polynomial) \