OpenTitan_AES: Add AES CBC mode support

[rknastenka]

Description

This PR introduces Cipher Block Chaining (CBC) mode support to the OpenTitan_AES peripheral. It implements initialization vector (IV) register handling and proper integration with the underlying .NET cryptography engine.

Dependency Note

⚠️ Important: This PR is stacked directly on top of my previous bug fix in PR #205 (which addresses the underlying 128-bit vs 256-bit key-slicing issue outlined in Issue renode/renode#914).

• If PR [#914] OpenTitan_AES: Slice key array to match requested key size #205 is reviewed and merged first, this PR will automatically update to show only the clean, isolated CBC diff.
• All 10 peripheral tests (including the original ECB tests and the new CBC NIST verification vectors) pass perfectly when both changes are active.

Changes

• OpenTitan_AES.cs:
  • Added CipherBlockChaining mode handling inside ConfigureAES().
  • Implemented internal IV tracking and automated register processing.
  • Explicitly configured PaddingMode.None to ensure hardware-accurate block alignment.
• OpenTitan_AES_Test.cs:
  • Added comprehensive 128-bit CBC test vector verification (ShouldEncryptInCBCModeWithNistVector) using official NIST SP 800-38A Example F.2.1 vectors.

How Has This Been Tested?

Ran the full OpenTitan_AES_Tests suite locally using the Release configuration:

dotnet test src/Infrastructure/src/Emulator/Peripherals/Test/PeripheralsTests/PeripheralsTests.csproj -c Release --filter "FullyQualifiedName~OpenTitan_AES_Tests" -p:SignAssembly=false