New IC3: factor solver initialization

[kroening]

Summary:

• split solver setup into named initialization helpers
• separate base CNF setup, latch/input discovery, solver setup, and initial-state analysis
• keep the constructor logic behavior-preserving while making the setup flow clearer

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