rsensor 0.3.1

A packaging release; rsensor itself is unchanged from 0.3.0.

• The Flatpak builds against the freedesktop 25.08 runtime. The 24.08 one carries Rust 1.89, older than the compiler the dependency tree requires, so the manifest could not build at all
• Tagging now publishes a GitHub release carrying an Arch package and a Flatpak bundle, instead of leaving the tag with nothing behind it

Installing

# Arch (x86_64)
sudo pacman -U rsensor-0.3.1-1-x86_64.pkg.tar.zst

# Flatpak (x86_64; pulls the freedesktop 24.08 runtime from Flathub)
flatpak install --user rsensor-0.3.1-x86_64.flatpak

Building from source, or from the PKGBUILD in the repository, still
works the same way; see the README.