0007: Linux x86-64 first

Status: accepted.

Fastmash supports Linux x86-64 with glibc, and Windows through WSL2. Portable arithmetic already makes results independent of the platform, but process supervision, temporary files and signal handling are Linux-specific.

Support is kept to what can be tested and maintained with the hardware and continuous integration available to the project: current desktop and laptop Linux systems, one long-term-support Linux baseline for release binaries, and hosted CI. macOS on Apple Silicon is a later target, to be added when it can be built and tested on the same terms. Windows users run the Linux version through WSL2; native Windows is outside the current product scope.