Add legacy symmetric ciphers (TEA, RedPike, AveMaria), export them, fix selftest import, and make Hypothesis optional in fuzz tests

[SWORDIntel]

Motivation

• Provide interoperability/testing support for legacy block ciphers and a simple token substitution cipher used by historical tooling.
• Ensure local selftest.py can import the repository src package when run directly.
• Prevent test discovery failures on systems without hypothesis by adding a lightweight fallback so the test runner can still import the fuzz test module.

Description

• Added src/crypto_standalone/symmetric/legacy_ciphers.py implementing TEA, RedPike, and AveMariaCipher with block encrypt/decrypt and simple substitution encode/decode.
• Exported the new ciphers from src/crypto_standalone/symmetric/__init__.py and exposed them at the package top level in src/crypto_standalone/__init__.py.
• Added unit tests tests/unit/test_legacy_ciphers.py and tests/unit/test_ave_maria_cipher.py exercising known vectors, round-trip properties, validation errors, and simple token-preservation behavior.
• Made tests/adversarial/test_fuzz_hypothesis.py robust to missing hypothesis by adding a minimal stub implementation so the module can be imported when hypothesis is not installed.
• Updated selftest.py to insert the repository src directory into sys.path so local package imports work when running the script directly.

Testing

• Ran unit tests with pytest tests/unit -q and the new unit tests for TEA, RedPike, and AveMariaCipher completed successfully.
• Ran the adversarial fuzz test module import under CI-like environment and import succeeds both with and without hypothesis installed due to the added stub; pytest tests/adversarial/test_fuzz_hypothesis.py is skipped when hypothesis is not present.
• Executed selftest.py in a local dev environment and it successfully imported the crypto_standalone package using the injected src path.

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Codex Task