[dua] completely remove DUA features and configurations (#13191)

This commit removes the OPENTHREAD_CONFIG_TMF_PROXY_DUA_ENABLE feature
and all associated code, tests, CLI commands, and harness references.

Changes:
- Removed OPENTHREAD_CONFIG_TMF_PROXY_DUA_ENABLE definition and all
  assert/preprocessor checks.
- Completely deleted dua_manager.cpp and dua_manager.hpp.
- Removed DUA registration notifying and request URI paths.
- Cleaned up all references to Domain Unicast Address (DUA) across
  child management, notifier, time ticker, and MLE.
- Removed DUA commands and logic from the CLI and Python cert tests
  (including packet verifier).
- Verified that the entire codebase compiles clean and all tests
  successfully pass using the Nexus test suite.

tests/scripts/thread-cert/node.py

@@ -1616,32 +1616,6 @@ class NodeImpl:
         self.remove_prefix(prefix)
         self.register_netdata()
 
-    def set_next_dua_response(self, status: Union[str, int], iid=None):
-        # Convert 5.00 to COAP CODE 160
-        if isinstance(status, str):
-            assert '.' in status
-            status = status.split('.')
-            status = (int(status[0]) << 5) + int(status[1])
-
-        cmd = 'bbr mgmt dua {}'.format(status)
-        if iid is not None:
-            cmd += ' ' + str(iid)
-        self.send_command(cmd)
-        self._expect_done()
-
-    def set_dua_iid(self, iid: str):
-        assert len(iid) == 16
-        int(iid, 16)
-
-        cmd = 'dua iid {}'.format(iid)
-        self.send_command(cmd)
-        self._expect_done()
-
-    def clear_dua_iid(self):
-        cmd = 'dua iid clear'
-        self.send_command(cmd)
-        self._expect_done()
-
     def multicast_listener_list(self) -> Dict[IPv6Address, int]:
         cmd = 'bbr mgmt mlr listener'
         self.send_command(cmd)
@@ -2153,7 +2127,7 @@ class NodeImpl:
         omr_addrs = []
         for addr in self.get_addrs():
             for prefix in prefixes:
-                if (addr.startswith(prefix)) and (addr != self.__getDua()):
+                if addr.startswith(prefix):
                     omr_addrs.append(addr)
                     break
 
@@ -2202,13 +2176,6 @@ class NodeImpl:
 
         return None
 
-    def __getDua(self) -> Optional[str]:
-        for ip6Addr in self.get_addrs():
-            if re.match(config.DOMAIN_PREFIX_REGEX_PATTERN, ip6Addr, re.I):
-                return ip6Addr
-
-        return None
-
     def get_ip6_address_by_prefix(self, prefix: Union[str, IPv6Network]) -> List[IPv6Address]:
         """Get addresses matched with given prefix.
 
@@ -2244,8 +2211,6 @@ class NodeImpl:
             return self.__getAloc()
         elif address_type == config.ADDRESS_TYPE.ML_EID:
             return self.__getMleid()
-        elif address_type == config.ADDRESS_TYPE.DUA:
-            return self.__getDua()
         elif address_type == config.ADDRESS_TYPE.BACKBONE_GUA:
             return self._getBackboneGua()
         elif address_type == config.ADDRESS_TYPE.OMR: