Add pyrift — static analyser for silent CPython/PyPy behaviour differences

[BHUVANSH855]

pyrift is a static analysis tool that detects silent Python behaviour
differences across CPython versions and between CPython and PyPy.

These are patterns that linters, type checkers, and security scanners
all miss — they only appear at runtime.

• 90 rules (45 CPython version compatibility + 45 PyPy runtime differences)
• 392 tests passing on Python 3.10, 3.11, 3.12, 3.13
• Zero dependencies — pure Python
• MIT licensed
• CLI + Python API + pre-commit hook support
• Baseline engine and target-aware scanning

GitHub: https://github.com/BHUVANSH855/pyrift
PyPI: https://pypi.org/project/pyrift/

[mre]

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