Consider replacing/supplementing `common.hpp` with a meson configuration file

Something like
```meson
# Set up the configuration file
conf = configuration_data()
if cpp.has_type('ssize_t', prefix: '#include ')
conf.set('HAS_SSIZE_T', 1)
endif
configure_file(
input: 'dwave/optimization/include/dwave-optimization/config.hpp.in',
output: 'config.hpp',
configuration: conf,
)
```
with a
```c++
// config.hpp.in
#mesondefine HAS_SSIZE_T
```
which we can then include.

I think it may be possible to replace `common.hpp` entirely with this, but needs more thought/experimentation.

Start by inspecting common.hpp and the existing Meson setup, then compare it with the proposed dwave/optimization/include/dwave-optimization/config.hpp.in configuration flow. Determine whether Meson configuration can replace or should supplement common.hpp, and verify that the resulting configuration works across the supported build paths.

Written by the indexing model from the issue text.