Add abstract methods to BaseTzInfo

stubs/pytz/@tests/stubtest_allowlist.txt

@@ -0,0 +1,5 @@
+# "Abstract" methods, see the .pyi file for more details.
+pytz.BaseTzInfo.localize
+pytz.BaseTzInfo.normalize
+pytz.tzinfo.BaseTzInfo.localize
+pytz.tzinfo.BaseTzInfo.normalize

stubs/pytz/pytz/tzinfo.pyi

@@ -1,8 +1,21 @@
 import datetime
+from abc import abstractmethod
 from typing import Any
 
 class BaseTzInfo(datetime.tzinfo):
     zone: str | None  # Actually None but should be set on concrete subclasses
+    # The following abstract methods don't exist in the implementation, but
+    # are implemented by all sub-classes.
+    @abstractmethod
+    def localize(self, dt: datetime.datetime) -> datetime.datetime: ...
+    @abstractmethod
+    def normalize(self, dt: datetime.datetime) -> datetime.datetime: ...
+    @abstractmethod
+    def tzname(self, dt: datetime.datetime | None) -> str: ...
+    @abstractmethod
+    def utcoffset(self, dt: datetime.datetime | None) -> datetime.timedelta | None: ...
+    @abstractmethod
+    def dst(self, dt: datetime.datetime | None) -> datetime.timedelta | None: ...
 
 class StaticTzInfo(BaseTzInfo):
     def fromutc(self, dt: datetime.datetime) -> datetime.datetime: ...