docs: Modernize XML Documentation for Symmetric Infrastructure (Batch 4)

[KonradSop]

Description

Systematic modernization of API documentation for symmetric cryptographic modules.
Replaced legacy Java-style comments with professional C# XML documentation, specifically targeting:

• Buffered Block Ciphers: 100% coverage for BufferedBlockCipher.
• Block Cipher Modes: SIC/CTR, CFB, OFB including all Span overloads.
• Padding Schemes: PKCS7, ISO7816-4, X9.23 with detailed randomness behavior and Span support.
• Parameter Wrappers: Refined documentation for ParametersWithIV, ParametersWithSalt, ParametersWithID, ParametersWithRandom, ParametersWithSBox, and ParametersWithUKM.

Key Accomplishments

• Informativeness Audit: Moved beyond simple labels to "Premium Informatics" standards for <summary> and <returns>.
• Modern .NET Support: Added full XML documentation for Span<byte> and ReadOnlySpan<byte> infrastructure.
• Architectural Consistency: Standardized documentation across all symmetric parameter wrappers and internal accessors.

Verification

• Build Status: Succeeded (dotnet build).
• Quality Pass: Performed a file-by-file audit to ensure no documentation gaps or regressions.

Checklist before requesting a review

• I have performed a self-review of my code
• I have kept the patch limited to only change the parts related to the patch
• This change requires a documentation update

See also Contributing Guidelines.