fix(shellyctl): align PKGBUILD with Arch Go package guidelines

- Add prepare() with GOPATH and go mod download for reproducible builds
- Remove redundant CLI flags from go build, rely on GOFLAGS export
- Add GOPATH="${srcdir}" to build() as recommended by guidelines
- Add check() function running go test
- Fix license file permissions from 0755 to 0644

Co-authored-by: Copilot <copilot@github.com>

PKGBUILD

@@ -15,6 +15,19 @@ source=(
 sha512sums=('2c19275204461c0449f4e638cbde8722a0387b147eaa77e2091d160b8c1233d061170ff3600293d116d1740166dacac3cc3ce79549f4558ed8adc5eb45efe224')
 b2sums=('a525fc326b8435c936798214911417cca29251062aa968753d0f2f68eee188e66bf5dca16489cb7fd51818389e931e3d9cdf67376968255ab008a602982845a0')
 
+prepare() {
+  cd "$pkgname-$pkgver"
+
+  export GONOSUMDB="${GONOSUMDB}"
+  export GOPATH="${srcdir}"
+  export GOPROXY="${GOPROXY}"
+
+  # INFO: Print all Go related environment variables for debugging purposes.
+  env | sort | grep -E '^C?GO'
+
+  go mod download -modcacherw
+}
+
 build() {
   cd "$pkgname-$pkgver"
 
@@ -23,16 +36,15 @@ build() {
   export CGO_CFLAGS="${CFLAGS}"
   export CGO_CXXFLAGS="${CXXFLAGS}"
   export CGO_LDFLAGS="${LDFLAGS}"
+  export GOPATH="${srcdir}"
   export GOFLAGS="-buildmode=pie -trimpath -ldflags=-linkmode=external -mod=readonly -modcacherw"
 
-  go build -v \
-    -trimpath \
-    -buildmode=pie \
-    -mod=readonly \
-    -modcacherw \
-    -ldflags "-linkmode external -extldflags \"${LDFLAGS}\"" \
-    -o $pkgname \
-    .
+  go build -o $pkgname .
+}
+
+check() {
+  cd "$pkgname-$pkgver"
+  go test ./...
 }
 
 package() {
@@ -40,5 +52,5 @@ package() {
   install -D --mode 0755 --target-directory "$pkgdir/usr/bin" "$pkgname-$pkgver/$pkgname"
 
   # license
-  install -D --mode 0755 --target-directory "$pkgdir/usr/share/licenses/$pkgname" "$pkgname-$pkgver/LICENSE.md"
+  install -D --mode 0644 --target-directory "$pkgdir/usr/share/licenses/$pkgname" "$pkgname-$pkgver/LICENSE.md"
 }