[mypyc] Record MRO ancestor modules as deps of subclass-defining modules

[geooo109]

(Context: surfaced by this sqlglot CI failure)

Mypy's incremental system only recompiles a module when a recorded dependency changes, and a dependency edge to an ancestor's module is created in cases such as an explicit import or a checked expression whose type references that ancestor. A bare subclass definition produces neither, so the transitive ancestors never enter the module's dependency graph:

# a.py
class A:
    def foo1(self) -> int: ...
    def foo2(self) -> int ... <- we remove this method

# b.py
from a import A
class B(A):
    def other(self) -> str: ...

# c.py
from b import B
class C(B): pass <- no dependecy on A, only on B

For type checking ^ is fine: a change in a distant ancestor doesn't affect the subclass's interface. But mypyc's generated C embeds the full layout of every ancestor into the subclass, including a vtable slot for each inherited method and struct offsets for inherited attributes. Thus, the generated C depends on ancestors that the dependency graph doesn't capture.

The goal of this PR is to make the dependency graph reflect what the generated C actually depends on. When compiling with mypyc, a module that defines a class now records the modules defining every ancestor in that class's MRO as indirect dependencies, so an ancestor's interface change reaches the subclass-defining module directly.