Restructure2

[ezander]

Restructure and modernize dvrlib

This branch restructures the project layout, improves code quality, and extends tooling.

Project structure

• Moved tests to test/, demo to demo/; library sources stay in src/
• Migrated test suite from hand-rolled functions to Catch2 v3 (via FetchContent) with a custom listener
  for per-test colored output
• Added a VDI2048 regression test with hardcoded expected values

Code quality

• Removed inheritance of vector_view/matrix_view from vector/matrix (Liskov violation); views are now
  standalone classes with operator vector()/operator matrix() for copy-out
• Fixed narrowing conversions, replaced 0 with nullptr, named the magic constant 1.96 as z_alpha_95 =
  Φ⁻¹(0.975)
• Added .clang-tidy and .editorconfig; unified code style to 2-space indent throughout

Build and tooling

• Added Makefile with targets: all, run-tests, run-demo, run-coverage, run-coverage-html, check, clean
• check target runs clang-format in dry-run mode
• Coverage via gcov (console summary) and optionally lcov (HTML report)
• Updated CI workflow to use make run-tests

Demo

• Reworked VDI2048 demo to follow the standard appendix more closely, with --keep-free flag to select the
  Z-algorithm variant and a side-by-side comparison target (run-demo-compare)