psycopg2: Fix missing Protocol base class in file protocols

This is an error I introduced in python#10630 because I didn't know protocols
need to be explicitly inherited from in other protocol subclasses.

The added test shows the change. Basically these protocols were unusable.

stubs/psycopg2/@tests/test_cases/check_extensions.py

@@ -1,5 +1,6 @@
 from __future__ import annotations
 
+import io
 from typing_extensions import assert_type
 
 import psycopg2.extensions
@@ -54,3 +55,8 @@ class MyCursor(psycopg2.extensions.cursor):
 assert_type(dconn.cursor("test-dcur", None), psycopg2.extras.DictCursor)
 assert_type(dconn.cursor("test-dcur", cursor_factory=None), psycopg2.extras.DictCursor)
 assert_type(dconn.cursor("test-dcur", cursor_factory=MyCursor), MyCursor)
+
+# file protocols
+# --------------
+cur = conn.cursor()
+cur.copy_from(io.StringIO(), "table")

stubs/psycopg2/psycopg2/_psycopg.pyi

@@ -83,8 +83,8 @@ threadsafety: int
 
 __libpq_version__: int
 
-class _SupportsReadAndReadline(SupportsRead[str], SupportsReadline[str]): ...
-class _SupportsReadAndReadlineAndWrite(_SupportsReadAndReadline, SupportsWrite[str]): ...
+class _SupportsReadAndReadline(SupportsRead[str], SupportsReadline[str], Protocol): ...
+class _SupportsReadAndReadlineAndWrite(_SupportsReadAndReadline, SupportsWrite[str], Protocol): ...
 
 class cursor:
     arraysize: int