[dua] remove OPENTHREAD_CONFIG_DUA_ENABLE build feature (#13165)

This commit completely removes the local Domain Unicast Address (DUA)
registration feature flag (OPENTHREAD_CONFIG_DUA_ENABLE) and all of
its associated implementation, public APIs, CLI commands, Spinel
property handlers, and certification tests.

Thread 1.2 FTD Border Router/Router DUA proxying features for MTD
children (OPENTHREAD_CONFIG_TMF_PROXY_DUA_ENABLE) are preserved and
updated to only compile/instantiate components when proxy DUA
features are active.

Detailed Changes:
- Remove default definition of OPENTHREAD_CONFIG_DUA_ENABLE from
  misc.h.
- Remove OT_DUA and openthread_config_dua_enable from CMake/GN
  configs.
- Remove otThreadSetFixedDuaInterfaceIdentifier and
  otThreadGetFixedDuaInterfaceIdentifier from
  include/openthread/thread.h
  and implementation src/core/api/thread_api.cpp.
- Remove CLI DUA interpreter from src/cli/cli.cpp.
- Remove SPINEL_CAP_DUA capability and SPINEL_PROP_THREAD_DUA_ID
  Spinel property handlers and dispatchers from NCP.
- Strip local DUA management features (conflict checking, SLAAC DUA
  interface identifiers, and dad info settings) from DuaManager, MLE,
  Address Resolver, and settings.
- Clean up Notifier, TimeTicker, and TMF dispatcher guards.
- Clean up -DOT_DUA=ON compilation flags across build/test scripts.
- Delete obsolete DUA certification tests:
  - v1_2_test_domain_unicast_address
  - v1_2_test_domain_unicast_address_registration
  - v1_2_test_dua_handle_address_error

script/test

@@ -125,7 +125,6 @@ build_simulation()
     fi
 
     if [[ ${version} != "1.1" ]]; then
-        options+=("-DOT_DUA=ON")
         options+=("-DOT_MLR=ON")
     fi
 
@@ -184,7 +183,6 @@ build_posix()
     )
 
     if [[ ${version} != "1.1" ]]; then
-        options+=("-DOT_DUA=ON")
         options+=("-DOT_MLR=ON")
         options+=("-DOT_LINK_METRICS_INITIATOR=ON")
         options+=("-DOT_LINK_METRICS_SUBJECT=ON")
@@ -346,7 +344,6 @@ do_build_otbr_docker()
         "-DOT_ANYCAST_LOCATOR=ON"
         "-DOT_COVERAGE=ON"
         "-DOT_DNS_CLIENT=ON"
-        "-DOT_DUA=ON"
         "-DOT_MLR=ON"
         "-DOT_NETDATA_PUBLISHER=ON"
         "-DOT_SLAAC=ON"