Introduced unconditional hard dependency on typing_extensions (Starlette 0.35)

[palankai]

Hi,

Starlette 0.35 cannot be used with Python> 3.9 because of hard dependency on not installed typed_extensions.

The typing_extension package is a conditional requirement according to pyproject.toml
https://github.com/encode/starlette/blob/0.35.0/pyproject.toml#L32

However, application.py requires it unconditionally:
https://github.com/encode/starlette/blob/0.35.0/starlette/applications.py#L6

I suggest to follow how it is imported in authentication.py:
https://github.com/encode/starlette/blob/0.35.0/starlette/authentication.py#L7

The error:

Traceback (most recent call last):
  File "/opt/src/main.py", line 7, in <module>
    from starlette.applications import Starlette
  File "/usr/local/lib/python3.12/site-packages/starlette/applications.py", line 6, in <module>
    from typing_extensions import ParamSpec
ModuleNotFoundError: No module named 'typing_extensions'

The bug (I think that can be classified as such) was introduced:
866a15f

My application is a fairly "vanilla" small Startlette-based API running in docker with Python 3.12.1

A possible workaround is installing typing_extensions separately.
(I'd rather pin down Startlett for the time being starlette!=0.35.0 for project using Python >= 3.10)

[Kludex]

PR welcome.

[Kludex]

Released: #2410

Sorry for the trouble.