Modernize build process

[jleben]

Changes:

• A CMakePresets.json file is added with presets for Linux and MacOS (the latter is a placeholder as MacOS is not yet fully supported).
• Build configuration is adjusted to enable lockfree 128-bit atomics on 64-bit Intel architecture
  • using Clang compiler
  • using the libc++ standard library implementation
  • adding the -mcx16 compiler flag
• C++ standard is raised to C++23 and a few necessary code adjustments are made.
• README.md is expanded with information on building Stitch, including implications for lock-freedom of some build configurations.

[jleben]

Test names needed to be changed when raising the C++ standard level - the empty symbol clashed with parts of standard library, causing a misleading error.

[jleben]

Just silencing some compiler warnings about an unused variable here.