PY-20611 Missing warning about functions implicitly returning None when return type is not Optional

Updated PyFunction to account for implicit 'return None' statements when inferring return statement types.

It affected return type inference of PyFunction.

Fixed a failing test related to formatted strings.

Added a quick fix to make all return statements explicit.

Updated the CFG to include PyPassStatements, enabling detection of exit points in empty functions.

Simplified PyMakeFunctionReturnTypeQuickFix to independently infer function types and handle required imports. Currently, it does not support specifying custom suggested types.



Merge-request: IJ-MR-148719
Merged-by: Aleksandr Govenko <aleksandr.govenko@jetbrains.com>

GitOrigin-RevId: 9f58961f9eb70e4f9dbba7359f5aafdfd392b7e2

python/testData/quickFixes/PyMakeFunctionReturnTypeQuickFixTest/ancestorAndInheritorReturn/main_after.py

@@ -1,10 +1,10 @@
 from typing import Type
 
 import my
-from my import X
+from my import X, Y
 
 
-def foo(a) -> Type[X]:
+def foo(a) -> Type[X | Y]:
     if a:
         return my.X<caret>
     else:

python/testData/quickFixes/PyMakeReturnsExplicitFixTest/addReturnsFromReturnStmt.py

@@ -0,0 +1,7 @@
+def f(x) -> int | None:
+    if x == 1:
+        return 42
+    elif x == 2:
+        <warning descr="Function returning 'int | None' has implicit 'return None'">return<caret></warning>
+    elif x == 3:
+        pass

python/testData/quickFixes/PyMakeReturnsExplicitFixTest/addReturnsFromReturnStmt_after.py

@@ -0,0 +1,8 @@
+def f(x) -> int | None:
+    if x == 1:
+        return 42
+    elif x == 2:
+        return None
+    elif x == 3:
+        return None
+    return None