) (#37802)

This PR adds templating for Python versions and updates the maximum
supported Python version to 3.13. The following major changes related to
templating are added:
- Minimum supported Python version and list of supported versions in
`setup.py` are fetched using new template generated files called
`python_version.py`
- Dockerfiles for the different Python Linux builds are now template
generated.
- The "Supported Python Versions" section from READMEs of ancillary and
main packages have been removed

Note: All the `python_version.py` files and Linux build `Dockerfiles`
except `tools/dockerfile/grpc_artifact_python_linux_armv7/Dockerfile` in
the PR are generated from the respective templates.

Further non-templated additions to add support for Python 3.13:
- install scripts and artifacts for windows, macos and linux are added
manually. Later, these can be templated as well.
 - updated cython bounds to 3.x
- updated twine version to solve [cgi module import
error](pypa/twine#1046)
- the twine update introduces a dependency on cryptography>=2.0. But the
cryptography package doesn't support 32-bit Linux images and hence
`twine check` has been disabled for x86 manylinux and x86 musllinux
artifacts.

Closes #37643

PiperOrigin-RevId: 678954495




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…rs (#37807) (#37809)

Building armv7 artifacts after adding Python 3.13 is failing with a
timeout. Hence increasing timeout to 2 hours.

Change was created by the release automation script. See go/grpc-release

#38632)

Backport #38613 to v1.66.x

Based on the
[spec](https://github.com/grpc/grpc/blob/master/doc/xds-test-descriptions.md#server)
and the [reference Java
implementation](https://github.com/grpc/grpc-java/blob/master/interop-testing/src/main/java/io/grpc/testing/integration/XdsTestClient.java),
it's the server that needs to honor the "keep-open" behavior and not the
client.

(I'm not changing the server's behavior in this PR, since we are not
using C++ servers and instead using Java servers for the concerned
tests.)

…#39335)

Backport of #38894 to v1.66.x.
---
With the current setting of 120 minutes there is the occassional timeout
error.

… vm - 1 (#39387)

*Beep boop. This is an automatically generated backport of #38967.*

Co-authored-by: Pawan Bhardwaj <bpawan@google.com>