VecMem Beta 0.23.0

Release including the following update(s) since v0.22.0:

• Introduced Doxygen documentation building for the project;
• Made all remaining 64->32 bit conversions explicit in the code to avoid compiler warnings;
• Made the atomic operation tests a bit more elaborate in device code, to help with debugging some remaining issues in Intel's SYCL compiler;
• Made it possible to build the (SYCL sources of the) project using icx-cl.exe on Windows;
• Made the vecmem::data::jagged_vector_buffer constructors accept not just std::size_t, but other unsigned integral type "size vectors" as well.