internal/rosa: wrap per-arch values

This is cleaner syntax in some specific cases.

Signed-off-by: Ophestra <cat@gensokyo.uk>

internal/rosa/rosa.go

@@ -69,6 +69,18 @@ func triplet() string {
 	return linuxArch() + "-rosa-linux-musl"
 }
 
+// perArch is a value that differs per architecture.
+type perArch[T any] map[string]T
+
+// unwrap returns the value for the current architecture.
+func (p perArch[T]) unwrap() T {
+	v, ok := p[runtime.GOARCH]
+	if !ok {
+		panic("unsupported target " + runtime.GOARCH)
+	}
+	return v
+}
+
 const (
 	// EnvTriplet holds the return value of triplet.
 	EnvTriplet = "ROSA_TRIPLE"