[BUG] set_cover Python: 整数焦点超载无法访问,且 bool in_focus 标志在新的不变量上导致 GreedySolutionGenerator 发生崩溃

inv.compute_coverage_in_focus([0, 1, 2]) TypeError: compute_coverage_in_focus(): incompatible function arguments. The following argument types are supported:

1. (self: ...SetCoverInvariant, focus: absl::lts_20250814::Span) -> list[int] pybind11 falling back to the raw C++ type name in the signature is the tell: nothing is registered for absl::Span, so no Python object can satisfy the parameter. set_cover.cc includes pybind11/stl.h and pybind11_protobuf/native_proto_caster.h, neither of which provides abseil casters.