ci: attach .deb and .rpm packages to releases and nightlies

Built by nfpm from the static musl binaries, with the man page and the
bash, zsh and fish completions. The names carry no version, so
releases/latest/download/soulseek-rs-amd64.deb stays a working link; the
nightly pair replaces itself on the rolling prerelease.

scripts/package-linux.sh

@@ -0,0 +1,54 @@
+#!/bin/sh
+set -eu
+umask 022
+
+[ $# -ge 4 ] || {
+  echo "usage: $0 <binary> <version> <target-triple> <out-dir> [<package-basename>]" >&2
+  exit 2
+}
+
+NFPM_VERSION=2.47.0
+
+binary=$1
+PKG_VERSION=$2
+target=$3
+out=$4
+package=${5:-soulseek-rs}
+
+case "$target" in
+  x86_64-*) PKG_ARCH=amd64 rpm_arch=x86_64 ;;
+  aarch64-*) PKG_ARCH=arm64 rpm_arch=aarch64 ;;
+  *) echo "no package architecture for $target" >&2; exit 1 ;;
+esac
+
+case "$(uname -s)-$(uname -m)" in
+  Linux-x86_64) nfpm_asset=Linux_x86_64 nfpm_sha256=0660ca602b2d2d2ae4781a06c692b3eeb9d437ffea05b831d76e41f4a3188783 ;;
+  Linux-aarch64) nfpm_asset=Linux_arm64 nfpm_sha256=1c0f5f2999b9a974bfb04fdb0cc3306096de530ac5dbb25d739cc5f5219c919c ;;
+  *) echo "no pinned nfpm build for this machine" >&2; exit 1 ;;
+esac
+
+root=$(cd "$(dirname "$0")/.." && pwd)
+work=$(mktemp -d)
+trap 'rm -rf "$work"' EXIT
+stage=$root/target/nfpm
+rm -rf "$stage"
+mkdir -p "$stage" "$out"
+out=$(cd "$out" && pwd)
+
+cp "$binary" "$stage/soulseek-rs"
+"$binary" completions print bash > "$stage/soulseek-rs.bash"
+"$binary" completions print zsh > "$stage/_soulseek-rs"
+"$binary" completions print fish > "$stage/soulseek-rs.fish"
+"$binary" man > "$stage/soulseek-rs.1"
+gzip -9n "$stage/soulseek-rs.1"
+
+archive=nfpm_${NFPM_VERSION}_$nfpm_asset.tar.gz
+curl -fsSL -o "$work/$archive" \
+  "https://github.com/goreleaser/nfpm/releases/download/v$NFPM_VERSION/$archive"
+echo "$nfpm_sha256  $work/$archive" | sha256sum -c - >/dev/null
+tar -xzf "$work/$archive" -C "$work" nfpm
+
+export PKG_ARCH PKG_VERSION
+cd "$root"
+"$work/nfpm" package --config packaging/nfpm.yaml --packager deb --target "$out/$package-$PKG_ARCH.deb"
+"$work/nfpm" package --config packaging/nfpm.yaml --packager rpm --target "$out/$package-$rpm_arch.rpm"