Phase 1 of the theory_nseq implementation: a stub theory solver for
strings based on Nielsen transformations and lazy regex membership.
- New files: theory_nseq.h/cpp with all required theory virtual methods
- Add 'nseq' to smt.string_solver parameter validation and documentation
- Wire into smt_setup.cpp dispatch (setup_QF_S, setup_seq_str, setup_nseq)
- Currently returns FC_GIVEUP for non-trivial string constraints
Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>