feat: add comprehensive DNS handler e2e tests

Adds 22 DNS e2e subtests across 8 test methods covering: upstream
resolution (A, AAAA, multi-A), TCP mode, bypass rules, host mapper,
exchange failure (graceful error recovery), rate limiter wiring,
invalid query handling, and DNS over TLS (mode: tls).

Includes two authoritative DNS responders (UDP/TCP), a standalone
DNS query client, and a TLS DNS query script.

tests/e2e/testdata/dns/server_bypass.yaml

@@ -0,0 +1,16 @@
+services:
+- name: dns
+  addr: :1053
+  handler:
+    type: dns
+    metadata:
+      dns: udp://dns-server:5353
+      timeout: 5s
+  listener:
+    type: dns
+  bypass: block-example
+
+bypasses:
+- name: block-example
+  matchers:
+  - test.example.com

tests/e2e/testdata/dns/server_exchange_failure.yaml

@@ -0,0 +1,10 @@
+services:
+- name: dns
+  addr: :1053
+  handler:
+    type: dns
+    metadata:
+      dns: udp://127.0.0.1:1
+      timeout: 2s
+  listener:
+    type: dns

tests/e2e/testdata/dns/server_hosts.yaml

@@ -0,0 +1,19 @@
+services:
+- name: dns
+  addr: :1053
+  handler:
+    type: dns
+    metadata:
+      # No upstream — host mapper resolves before exchanger is ever reached.
+      timeout: 2s
+  listener:
+    type: dns
+  hosts: my-hosts
+
+hosts:
+- name: my-hosts
+  mappings:
+  - ip: 10.0.0.100
+    hostname: mapped.example.com
+  - ip: 192.168.1.200
+    hostname: aaaa.mapped.example.com

tests/e2e/testdata/dns/server_rlimiter.yaml

@@ -0,0 +1,16 @@
+services:
+- name: dns
+  addr: :1053
+  handler:
+    type: dns
+    metadata:
+      dns: udp://dns-server:5353
+      timeout: 5s
+  listener:
+    type: dns
+  rlimiter: limiter-0
+
+rlimiters:
+- name: limiter-0
+  limits:
+  - "$ 1000"

tests/e2e/testdata/dns/server_tcp.yaml

@@ -0,0 +1,12 @@
+services:
+- name: dns
+  addr: :1053
+  handler:
+    type: dns
+    metadata:
+      dns: tcp://dns-server:5353
+      timeout: 5s
+  listener:
+    type: dns
+    metadata:
+      mode: tcp

tests/e2e/testdata/dns/server_tls.yaml

@@ -0,0 +1,12 @@
+services:
+- name: dns
+  addr: :1053
+  handler:
+    type: dns
+    metadata:
+      dns: udp://dns-server:5353
+      timeout: 5s
+  listener:
+    type: dns
+    metadata:
+      mode: tls

tests/e2e/testdata/dns/server_upstream.yaml

@@ -0,0 +1,10 @@
+services:
+- name: dns
+  addr: :1053
+  handler:
+    type: dns
+    metadata:
+      dns: udp://dns-server:5353
+      timeout: 5s
+  listener:
+    type: dns