New IC3: extract blocking phase

[kroening]

Summary:

• extract the frame-blocking loop into a dedicated helper
• keep the top-level solve loop focused on frame creation, progress reporting, and propagation
• preserve the existing obligation-processing behavior while clarifying the phase split

Verification:

• make -C src/new-ic3 CXX='ccache clang++' CCACHE_DIR=/tmp/ccache-hw
• make -C src/ebmc CXX='ccache clang++' CCACHE_DIR=/tmp/ccache-hw
• ./src/ebmc/ebmc regression/ebmc/new-ic3/proved1.sv --new-ic3 --property main.p0
• ./src/ebmc/ebmc regression/ebmc/new-ic3/refuted1.sv --new-ic3 --top main
• ./src/ebmc/ebmc regression/ebmc/new-ic3/cover1.sv --new-ic3 --top main