Implement AES-IGE and MTProto package structure

[SWORDIntel]

Implemented AES-IGE mode in pure Python following the project's rigid constraints and structured the MTProto subpackage layout.

• Modified AES256 to a generalized AES cipher capable of 128, 192, and 256-bit encryption (based on key length), retaining perfect backward compatibility with existing AES tests.
• Created AESIGE implementing Infinite Garble Extension via the 32-byte two-block IV recurrence standard.
• Implemented robust defensive input validation for AES-IGE (strictly block aligned).
• Formed the src/crypto_standalone/mtproto/ skeleton featuring config.py (with dataclass limits), session.py (for the state structure and sequence bounding), and transport architectures.
• Added comprehensive unit testing verifying test vectors matching OpenSSL implementations, plus tests covering empty values, exceptions on bad sizes, multiblock roundtripping, and tampering.
• Updated docs/IMPLEMENTATION.md explicitly capturing the cryptographic limitations (confidentiality only, non-constant-time) and examples.
• Added performance benchmarks.

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PR created automatically by Jules for task 16354817585876427839 started by @SWORDIntel

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