…ation (#1590)

This PR drops the dependency on `cachetools`, which was only used for
its LRU cache class, in favor of a simple local implementation.

This should have a small but positive effect on many downstream users
given how many times this library is downloaded per day.

---------

Co-authored-by: Chalmer Lowe <[email protected]>

There were recently some type annotation changes that weren't compatible
with python 3.8. This PR fixes those, and adds back 3.8 tests using
github actions

---------

Co-authored-by: Anthonios Partheniou <[email protected]>

Removing support for EOL Python 3.7. 

A warning was present in the README that support would be removed after
January 2024

Also added a warning that Python 3.8 and 3.9 are also EOL, and will be
removed in future updates

---------

Co-authored-by: Victor Chudnovsky <[email protected]>

PR created by the Librarian CLI to initialize a release. Merging this PR
will auto trigger a release.

Librarian Version: v1.0.1
Language Image:
us-central1-docker.pkg.dev/cloud-sdk-librarian-prod/images-prod/python-librarian-generator@sha256:b8058df4c45e9a6e07f6b4d65b458d0d059241dd34c814f151c8bf6b89211209
<details><summary>google-auth: 2.47.0</summary>

##
[2.47.0](v2.46.0...v2.47.0)
(2026-01-06)

### Features

* drop `cachetools` dependency in favor of simple local implementation
(#1590)
([5c07e1c](5c07e1c4))

### Bug Fixes

* Python 3.8 support (#1918)
([60dc200](60dc2001))

</details>