Python 3.11 (#9515)

## Problem

On Debian 12 (Bookworm), Python 3.11 is the latest available version.

## Summary of changes
- Update Python to 3.11 in build-tools
- Fix ruff check / format
- Fix mypy
- Use `StrEnum` instead of pair `str`, `Enum`
- Update docs

test_runner/fixtures/utils.py

@@ -8,10 +8,10 @@ import subprocess
 import tarfile
 import threading
 import time
-from collections.abc import Iterable
+from collections.abc import Callable, Iterable
 from hashlib import sha256
 from pathlib import Path
-from typing import TYPE_CHECKING, Any, Callable, TypeVar
+from typing import TYPE_CHECKING, Any, TypeVar
 from urllib.parse import urlencode
 
 import allure
@@ -29,7 +29,7 @@ from fixtures.pg_version import PgVersion
 
 if TYPE_CHECKING:
     from collections.abc import Iterable
-    from typing import IO, Optional
+    from typing import IO
 
     from fixtures.common_types import TimelineId
     from fixtures.neon_fixtures import PgBin
@@ -66,10 +66,10 @@ def subprocess_capture(
     echo_stderr: bool = False,
     echo_stdout: bool = False,
     capture_stdout: bool = False,
-    timeout: Optional[float] = None,
+    timeout: float | None = None,
     with_command_header: bool = True,
     **popen_kwargs: Any,
-) -> tuple[str, Optional[str], int]:
+) -> tuple[str, str | None, int]:
     """Run a process and bifurcate its output to files and the `log` logger
 
     stderr and stdout are always captured in files.  They are also optionally
@@ -536,7 +536,7 @@ def assert_pageserver_backups_equal(left: Path, right: Path, skip_files: set[str
     """
     started_at = time.time()
 
-    def hash_extracted(reader: Optional[IO[bytes]]) -> bytes:
+    def hash_extracted(reader: IO[bytes] | None) -> bytes:
         assert reader is not None
         digest = sha256(usedforsecurity=False)
         while True:
@@ -563,7 +563,7 @@ def assert_pageserver_backups_equal(left: Path, right: Path, skip_files: set[str
 
     mismatching: set[str] = set()
 
-    for left_tuple, right_tuple in zip(left_list, right_list):
+    for left_tuple, right_tuple in zip(left_list, right_list, strict=False):
         left_path, left_hash = left_tuple
         right_path, right_hash = right_tuple
         assert (
@@ -595,7 +595,7 @@ class PropagatingThread(threading.Thread):
             self.exc = e
 
     @override
-    def join(self, timeout: Optional[float] = None) -> Any:
+    def join(self, timeout: float | None = None) -> Any:
         super().join(timeout)
         if self.exc:
             raise self.exc