Add legacy cipher modules (TEA, RedPike, AveMaria) and expose modular legacy import; update README and tests

[SWORDIntel]

Motivation

• Provide backward-compatible implementations of legacy ciphers for interoperability and migration workflows.
• Allow importing individual legacy cipher implementations from their own modules instead of a single monolithic implementation file.

Description

• Added new modules src/crypto_standalone/symmetric/tea.py, src/crypto_standalone/symmetric/redpike.py, and src/crypto_standalone/symmetric/avemaria.py implementing TEA, RedPike, and AveMariaCipher respectively with input validation and block/phrase encrypt/decrypt APIs.
• Refactored src/crypto_standalone/symmetric/legacy_ciphers.py into a thin aggregator that re-exports TEA, RedPike, and AveMariaCipher via __all__.
• Updated README.md to document the Legacy Ciphers (Interoperability Only) usage pattern and to advise against using these for new systems.
• Extended tests/unit/test_legacy_ciphers.py with TestModularUsageAndCompatibility tests that verify single-module imports and parse the new source files with ast.parse(..., feature_version=(3, 7)) to ensure Python 3.7 syntax compatibility.

Testing

• Ran the updated legacy cipher unit tests in tests/unit/test_legacy_ciphers.py with pytest and the tests completed successfully.
• Ran the repository unit test suite with pytest -q and the test run passed without failures.

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Codex Task