test(fixtures): add Arch package fixtures and prove Lua cross-validation probe

Ultraworked with [Sisyphus](https://github.com/code-yeongyu/oh-my-openagent)

Co-authored-by: Sisyphus <[email protected]>

testdata/srcinfo/vcs/PKGBUILD

@@ -0,0 +1,24 @@
+pkgname=mygit
+pkgver=r1.abc
+pkgrel=1
+pkgdesc="VCS package example"
+arch=(x86_64)
+url="https://example.org"
+depends=('git')
+source=("git+https://example.org/repo.git")
+sha256sums=('SKIP')
+
+pkgver() {
+  cd "$srcdir/repo"
+  git describe --long --tags | sed 's/^v//;s/\([^-]*-g\)/r\1/;s/-/./g'
+}
+
+build() {
+  cd "$srcdir/repo"
+  make
+}
+
+package() {
+  cd "$srcdir/repo"
+  make DESTDIR="$pkgdir" install
+}