Clean-up dependencies

[20DM]

This change set is to

• make sure the package can be built with Conan v2
• make sure the package can be built with vanilla CMake (+ dependencies from homebrew on MacOS)
• get rid off GreatCMakeCookOff
• upgrades a few dependencies to more modern versions, incl. eigen/3.4.0, catch2/3.4.0, spdlog/1.12.0
• add code tweaks to support interface changes in Catch2
• add code tweaks to get rid off C++ compile time warnings
• keep the README in sync.

Closes #331 Closes #298 Closes #290 Closes #288

Goes hand-in-hand with https://github.com/astro-informatics/sopt/pull/418