Update ruff configuration to apply pyupgrade to modernize python syntax

[maxrabin]

Description

This project targets Python v3.10+ but, in some places, uses outdated Python syntax.
This change adds the "pyupgrade" rule to the "ruff" configuration to have ruff automatically modernize the Python syntax where applicable. This is most noticeable in formatting strings (f"{myvar} style" instead of "% style" % myvar) and in typing (list instead of typing.List, str | None instead of Optional[str])

Related Issues

#1335

Documentation PR

Type of Change

Breaking change - if anyone was using this library in a project with Python version < 3.10 (if this was possible, I didn't check) then this change will definitely break for them. B

Testing

How have you tested the change? Verify that the changes do not break functionality or introduce warnings in consuming repositories: agents-docs, agents-tools, agents-cli

• [v] I ran hatch run prepare

Checklist

• I have read the CONTRIBUTING document
• I have added any necessary tests that prove my fix is effective or my feature works
• I have updated the documentation accordingly
• I have added an appropriate example to the documentation to outline the feature, or no new docs are needed
• My changes generate no new warnings
• Any dependent changes have been merged and published

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[maxrabin]

I cannot split this into smaller Pull Requests. Its a one-line change in pyproject.toml to add "UP" in the ruff lint rules.
The rest are the result of running ruff via hatch.