[mdns] add native mDNS support in OT (#9797)

This commit introduces native mDNS support within the OpenThread
stack, implementing RFC 6762 compliant registration of hosts,
services, and keys. It supports the following functionalities:

- Sending probes to claim names.
- Sending announcements on initial registration and changes.
- Sending "goodbye" announcements when unregistered or upon record
  removal.
- Negative responses (NSEC).
- Support for service sub-types and their addition/removal.
- Support for `_services._dns-sd._udp` queries (all service types).
- Responding to queries (including "QU" questions).
- Delay mechanism when responding to multi-question query messages,
  ensuring unique answers.
- Providing extra records in the Additional Data section if not
  already in the Answer section (e.g., on a PTR query, include SRV
  and host AAAA addresses).
- Implementing Known-Answer Suppression.
- Supporting multi-packet queries with known answers in follow-up
  messages.
- Rate-limiting record multicasts (once per second).
- Rate-limiting probe responses (once per 250ms).
- Detecting conflicts after probes.
- Limiting the size of emitted responses or probes, breaking into
  multiple messages if necessary.
- Detecting self originating messages (sent by mDNS module).
- Support for service browser.
- Support for service resolvers (SRV and TXT records) and IPv4/IPv6
  address resolvers for hostnames.
- Introduces smart cache management:
  - Passively caches service records for active browsers.
  - Passively caches address records for active service resolvers.
- Enables multiple simultaneous browsers/resolvers for the same
  service/host.

This commit introduces public `otMdns` OpenThread APIs and related CLI
commands for the mDNS module.

For platform abstraction, `otPlatMdns` APIs are defined in
`mdns_socket.h` (e.g., to send or receive mDNS messages):

- An implementation of the platform APIs is provided for posix.
- Also under the simulation platform, a simplified implementation of the
  `otPlatMdns` APIs is provided (intended for testing).

This commit also adds a detailed `test_mdns` unit test, validating
various functionalities and covering potential edge cases.

tests/unit/test_platform.cpp

@@ -555,6 +555,35 @@ otError otPlatRadioSetCcaEnergyDetectThreshold(otInstance *aInstance, int8_t aTh
     return OT_ERROR_NONE;
 }
 
+#if OPENTHREAD_CONFIG_MULTICAST_DNS_ENABLE
+
+OT_TOOL_WEAK otError otPlatMdnsSetListeningEnabled(otInstance *aInstance, bool aEnable, uint32_t aInfraIfIndex)
+{
+    OT_UNUSED_VARIABLE(aInstance);
+    OT_UNUSED_VARIABLE(aEnable);
+    OT_UNUSED_VARIABLE(aInfraIfIndex);
+
+    return OT_ERROR_NOT_IMPLEMENTED;
+}
+
+OT_TOOL_WEAK void otPlatMdnsSendMulticast(otInstance *aInstance, otMessage *aMessage, uint32_t aInfraIfIndex)
+{
+    OT_UNUSED_VARIABLE(aInstance);
+    OT_UNUSED_VARIABLE(aMessage);
+    OT_UNUSED_VARIABLE(aInfraIfIndex);
+}
+
+OT_TOOL_WEAK void otPlatMdnsSendUnicast(otInstance                  *aInstance,
+                                        otMessage                   *aMessage,
+                                        const otPlatMdnsAddressInfo *aAddress)
+{
+    OT_UNUSED_VARIABLE(aInstance);
+    OT_UNUSED_VARIABLE(aMessage);
+    OT_UNUSED_VARIABLE(aAddress);
+}
+
+#endif // OPENTHREAD_CONFIG_MULTICAST_DNS_ENABLE
+
 #if OPENTHREAD_CONFIG_DNS_DSO_ENABLE
 
 OT_TOOL_WEAK void otPlatDsoEnableListening(otInstance *aInstance, bool aEnable)