build: bump python 3.13

[gsprochette]

Description

This PR bumps the max version of python to 3.13 and isolates realsrgan into its own extra since the setup of its basicsr dependency fails with the new python version.

Related Issue

Fixes #(issue number)

Type of Change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Refactor (no functional change)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Documentation update

Testing

• I added or updated tests covering my changes
• Existing tests pass locally (uv run pytest -m "cpu and not slow")

For full setup and testing instructions, see the Contributing Guide.

Checklist

• My code follows the style guidelines of this project
• I have performed a self-review of my code, especially for agent-assisted changes
• I updated the documentation where necessary

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[codacy-production]

Up to standards ✅

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[begumcig]

LET'S GOOOOOOOOOOOOOO

[github-actions]

This PR has been inactive for 10 days and is now marked as stale.