Dependency on `overrides` causes crash for Python 3.14

#### Description

Python 3.14 is scheduled to be released on Tuesday. (https://peps.python.org/pep-0745/) The dependency on `overrides` is a problem, as it raises an `AttributeError` when it is imported under Python 3.14. An [issue](https://github.com/mkorpela/overrides/issues/127) has been raised and a [pull request](https://github.com/mkorpela/overrides/pull/133) has been submitted to the GitHub repo for the `overrides` project. But the maintainer has been unresponsive.

---

#### Environment details

- OS type and version: `Any. Verified on Linux with x86_64 architecture`
- Python version: `Python 3.14.0rc2`
- pip version: `pip 24.3.1`
- `google-cloud-pubsublite` version: `Version: 1.12.0`

#### Steps to reproduce

```sh
git clone git@github.com:googleapis/python-pubsublite.git

cd python-pubsublite

uv venv --clear --python 3.14 && \
uv pip install -e . && \
uv run samples/snippets/list_lite_topics_example.py 1122334455 "us-central1" "a" True
```
```text
AttributeError: module 'typing' has no attribute 'ByteString'
```

#### Code example

Above, I'm just using the `list_lite_topics_example.py` in this repo's `samples/snippets/` directory

#### Stack trace
```
Traceback (most recent call last):
File "/mnt/md0/home/ed/Documents/python-pubsublite/samples/snippets/list_lite_topics_example.py", line 68, in
list_lite_topics(
~~~~~~~~~~~~~~~~^
args.project_number,
^^^^^^^^^^^^^^^^^^^^
...<2 lines>...
args.regional,
^^^^^^^^^^^^^^
)
^
File "/mnt/md0/home/ed/Documents/python-pubsublite/samples/snippets/list_lite_topics_example.py", line 27, in list_lite_topics
from google.cloud.pubsublite import AdminClient
File "/mnt/md0/home/ed/Documents/python-pubsublite/google/cloud/pubsublite/__init__.py", line 119, in
from google.cloud.pubsublite.admin_client import AdminClient
File "/mnt/md0/home/ed/Documents/python-pubsublite/google/cloud/pubsublite/admin_client.py", line 17, in
from overrides import overrides
File "/mnt/md0/home/ed/Documents/python-pubsublite/.venv/lib/python3.14/site-packages/overrides/__init__.py", line 8, in
from overrides.overrides import __VERSION__, overrides, override
File "/mnt/md0/home/ed/Documents/python-pubsublite/.venv/lib/python3.14/site-packages/overrides/overrides.py", line 26, in
from overrides.signature import ensure_signature_is_compatible
File "/mnt/md0/home/ed/Documents/python-pubsublite/.venv/lib/python3.14/site-packages/overrides/signature.py", line 6, in
from .typing_utils import get_args, issubtype
File "/mnt/md0/home/ed/Documents/python-pubsublite/.venv/lib/python3.14/site-packages/overrides/typing_utils.py", line 50, in
typing.ByteString: bytes, # https://docs.python.org/3/library/typing.html#typing.ByteString
^^^^^^^^^^^^^^^^^
File "/home/ed/.local/share/uv/python/cpython-3.14.0rc2-linux-x86_64-gnu/lib/python3.14/typing.py", line 3807, in __getattr__
raise AttributeError(f"module {__name__!r} has no attribute {attr!r}")
AttributeError: module 'typing' has no attribute 'ByteString'
```