feat!: remove MockTUFClient (#135)

* feat! remove MockTUFClient

*Breaking*
- use LocalPolicyDir and nil TUFClient instead

Other:
- add stateful Verifier

pkg/policy/testdata/policies/allow/doi/policy.rego

@@ -0,0 +1,7 @@
+package attest
+
+import rego.v1
+
+result := {
+  "success": true,
+}

pkg/policy/testdata/policies/allow/mapping.yaml

@@ -0,0 +1,17 @@
+# map repos to policies
+version: v1
+kind: policy-mapping
+policies:
+  - id: docker-official-images
+    description: Docker Official Images
+    attestations:
+      repo: "localhost:5001/library-refs"
+    files:
+      - path: doi/policy.rego
+rules:
+  - pattern: "^docker[.]io/library/(.*)$"
+    policy-id: docker-official-images
+  - pattern: ^localhost:5001/(.*)$
+    rewrite: docker.io/library/$1
+  - pattern: ^registry[.]local:5000/(.*)$
+    rewrite: docker.io/library/$1