Refactor cipher modes onto shared base classes; harden key wiping

[Xor-el]

Consolidate the BlockCipher modes and AEAD modes behind abstract base classes, deduplicating the surface each mode previously reimplemented while keeping every tuned hot path (SIMD/fused kernels, bulk batching, tag-lookahead buffering) in the concrete mode.

Base classes

• TAbstractBlockCipherMode: base for CBC, CFB, OFB, ECB, SIC and OpenPGP-CFB. Owns the underlying-cipher / algorithm-name / block-size accessors and one overflow-safe bulk bounds check (via TCheck).
• TAbstractAeadCipher + TAbstractAeadBlockCipher: bases for GCM, EAX, OCB, CCM, GCM-SIV and ChaCha20-Poly1305. Own GetMac, constant-time tag verification, the encrypt-side nonce-reuse guard, MAC-size validation, the unified MAC-check-failed error, the output-size template and a guaranteed key-wiping destructor.
• TGaloisFieldUtilities: single home for the GF(2^128) x-doubling that CMAC, EAX and OCB each duplicated. MulX moves into TGcmUtilities and ClpGcmSivUtilities is retired.

Security hardening

• Zeroize key-derived material on teardown for EAX, OCB, CCM, GCM-SIV and ChaCha20-Poly1305 (previously only GCM did). Notably, ChaCha's 256-bit key is now wiped.

Behavioural changes (intentional)

• GCM-SIV.GetMac now returns the stored tag instead of raising.
• The MAC-failure message is unified across all AEAD modes.

Tests

• Add an OpenPGP-CFB test: an independent first-block known-answer vector plus multi-length round-trips.

All cipher outputs remain byte-identical.