Setup: bump python & torch version

[Giuseppe5]

Reason for this PR

Python 3.8 has reached EOL

Changes Made in this PR

Minimum python version is now 3.9

Testing Summary

N A

Risk Highlight

• This PR includes code from another work (please detail).
• This PR contains API-breaking changes.
• This PR depends on work in another PR (please provide links/details).
• This PR introduces new dependencies (please detail).
• There are coverage gaps not covered by tests.
• Documentation updates required in subsequent PR.

Checklist

• Code comments added to any hard-to-understand areas, if applicable.
• Changes generate no new warnings.
• Updated any relevant tests, if applicable.
• No conflicts with destination dev branch.
• I reviewed my own code changes.
• Initial CI/CD passing.
• 1+ reviews given, and any review issues addressed and approved.
• Post-review full CI/CD passing.

[nickfraser]

Only one comment - should we use this moment to add some newer PT versions to the test suite?

[nickfraser]

Also, please close #959 when this gets merged.