feat: converter reads the Phone library's register statement, named stores and generators

`init phone register` becomes a default (the group chat) plus a function of library calls that runs with
the other defaults of a new game (phone_register.py). `init/python [early|hide] in some.store` wraps its
code in an in_store node and `default some.store.name` may name a store; yield works as an expression
(generator functions are marked gen); `import x as y`, `transform -150 name(...)`, `init:` with if/else,
`config.special_namespaces` lines, `at` lists and tuples, transforms made by Python functions, `choice`
weights that are expressions, `__len__`/`__bool__`, and the whitelist for os, calendar, itertools,
pygame_sdl2 and the new runtime. The converter also records the size of every picture it converts
(`imageSizes`) so `renpy.image_size` answers without loading.

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

backend/tests/test_compatibility.py

@@ -80,7 +80,7 @@ def test_renpy_only_declarations_are_not_execution_blockers(tmp_path):
 
 
 @pytest.mark.parametrize("source,reason", [
-    ('init python:\n    def helper():\n        received = yield 1\nlabel start:\n    $ helper()', "init python"),
+    ('init python:\n    def helper():\n        received = yield from other()\nlabel start:\n    $ helper()', "init python"),
     ('label start:\n    $ result = renpy.show_displayable("map")', "renpy.show_displayable"),
     ('label start:\n    jump missing', "missing"),
 ])