Resolve "Make chunk computations constexpr"
This MR implements the following changes:
- All arithmetic operations based on block sizes are now constexpr.
- Add several new functions, also constexpr: is_aligned(), is_power_of_2().
- Reimplement log2() to make it faster based on compiler builtins.
- Rename functions to avoid depending on the concept of chunk (in preparation for more chunk-agnostic code).
- Add exhaustive tests for all these functions and enable them in the CI.
- Rename the gkfs::util namespace to gkfs::utils.
- Create the gkfs::utils::arithmetic namespace for all these functions, as well as a convenience library/target in CMake for easier testing.