Core: add python 3.13 support (#5357)

* Core: fix freeze support for py3.13+

Loading Utils now patches multiprocessing.freeze_support()
Utils.freeze_support() is now deprecated

* WebHost: use pony fork on py3.13

* CI: test with py3.13

.github/workflows/unittests.yml

@@ -41,12 +41,13 @@ jobs:
         python:
           - {version: '3.11.2'} # Change to '3.11' around 2026-06-10
           - {version: '3.12'}
+          - {version: '3.13'}
         include:
           - python: {version: '3.11'}  # old compat
             os: windows-latest
-          - python: {version: '3.12'}  # current
+          - python: {version: '3.13'}  # current
             os: windows-latest
-          - python: {version: '3.12'}  # current
+          - python: {version: '3.13'}  # current
             os: macos-latest
 
     steps:
@@ -74,7 +75,7 @@ jobs:
         os:
           - ubuntu-latest
         python:
-          - {version: '3.12'}  # current
+          - {version: '3.13'}  # current
 
     steps:
     - uses: actions/checkout@v4