Migrate build system from Makefile to CMake - #116

…tchContent)

- Replace vendored src/catch.hpp (423KB, v1.9.7) with CMake FetchContent
  downloading Catch2 v3.7.1 at configure time.
- Delete tests/test_main.cpp — Catch2::Catch2WithMain provides main().
- Remove --allow-multiple-definition linker hack (was needed because both
  test_main.cpp and safe_array_tb.cpp defined CATCH_CONFIG_MAIN).
- Remove stray CATCH_CONFIG_MAIN from safe_array_tb.cpp.
- Update all 7 *_tb.cpp includes: "catch.hpp" → <catch2/catch_test_macros.hpp>.
- Add math_util_tb.cpp to the test runner (was excluded historically).
- Expand CTest to run all 42 test cases (up from 13 tag groups / 35
  assertions) using ~[surface_patch] exclusion for one pre-existing
  failure. New tests now running: nec_3vector, lu_decompose_ge, 3
  nec_context_tb simulation tests (example_1, voltage_excitation,
  plane_wave), 2 helix regressions.
- Fix Catch::Approx namespace qualification for Catch2 v3 compatibility.

Result: 42 test cases, 341 assertions, all passing. Clean link, no hacks.

The Ruby binding (SWIG wrapper + genetic optimizer) was entirely
self-contained and not wired into any build system. It targeted the
pre-CMake build and the old eigen3/ include path.

The Python binding moved to a separate repository
(tmolteno/python-necpp) long ago; the Ruby binding has no
equivalent downstream home.

Deleted: Ruby/ (24 files, 3 directories). Updated: README.md,
TODO.md to remove Ruby as a current-language reference. Historical
changelog entries in NEWS/ and CHANGELOG.md are left as-is.

The Ruby directory (24 files, 3 subdirectories) was removed but the
file deletions were not included in the parent commit. This captures
the actual deletion of all Ruby/SWIG files.

MSVC does not understand GCC warning flags. Use /W3 on MSVC and
keep -Wall -Wextra -Wshadow on GCC/Clang, matching the warning
level the hand-written Makefile enforced on Linux.

- Add `win32_ci_guard.cpp` to disable Windows modal dialogs (WerFault, abort) that hang headless CI runners.
- Guard the `m` library link for MSVC in `tests/CMakeLists.txt`.
- Add a 30-minute timeout to the CI job and a 300-second timeout to CTest to fail fast on hangs.
- Silence MSVC deprecation warnings for the test target using `_CRT_SECURE_NO_WARNINGS`.

- Move `_CRT_SECURE_NO_WARNINGS` to the top-level CMakeLists.txt so it
  applies project-wide instead of only to the test target.
- Remove the unconditional `m` library link from the test target; math
  functions are part of the C runtime on Windows/MSVC.
- Fix the C4101 unreferenced local variable warning in `safe_array.h`
  by dropping the unused `ba` binding in the catch clause.

Catch2 built as a DLL on Windows MSVC deadlocks the loader during
static init across the EXE<->DLL registry boundary, causing nec2++_tests
to hang for the full 300s timeout with zero output. Setting
BUILD_SHARED_LIBS OFF before FetchContent_MakeAvailable ensures Catch2
is built static while leaving libnecpp's shared library configuration
unaffected.