feat(dev): support development on darwin (OSX)

- Netlink linux tagged files
- Netlink linux || darwin tagged files
- Create non-implemented files for NOT linux
- Create non-implemented files for NOT linux and NOT darwin
- Specify wireguard netlink integration test as for linux only

internal/netlink/rule_unspecified.go

@@ -0,0 +1,19 @@
+//go:build !linux
+
+package netlink
+
+func NewRule() Rule {
+	return Rule{}
+}
+
+func (n *NetLink) RuleList(family int) (rules []Rule, err error) {
+	panic("not implemented")
+}
+
+func (n *NetLink) RuleAdd(rule Rule) error {
+	panic("not implemented")
+}
+
+func (n *NetLink) RuleDel(rule Rule) error {
+	panic("not implemented")
+}