[CTORNDGAIN-1179] Add Python 3.10+ version validation to run-test-cases.sh

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Jira Story

CTORNDGAIN-1179 — Add Python version validation to run-test-cases.sh

Summary

• Added an upfront Python 3.10+ guard to .github/scripts/run-test-cases.sh
• Checks for python3 presence via command -v python3 before any test execution
• Parses the version using python3 -c "import sys; ..." (same binary used later in the script)
• Exits with code 1 and a clear error message when python3 is missing or below 3.10
• Guard runs before changed=() initialization — before any file system or git operations
• Zero side effects on valid environments (Python 3.10+)

Testing Notes

• Missing python3: Script exits 1 with ERROR: python3 not found. Python 3.10+ is required.
• Wrong version (e.g. 3.9): Script exits 1 with ERROR: Python 3.10+ is required (found: 3.9). Please upgrade Python.
• Valid environment (3.10+): Script proceeds normally with no change in behaviour
• CI (validate-test-cases.yml) uses ubuntu-latest which ships Python 3.12 — no regression expected

Assumptions

• requires-python = ">=3.10" declared in all pyproject.toml files is the canonical version requirement
• No CI workflow YAML changes needed — the guard is transparent on conforming CI environments