docs: add XML documentation for CMS AuthenticatedData stream parser (Batch 15e)

[KonradSop]

Description

Adds XML documentation to CmsAuthenticatedDataParser — the streaming read-side counterpart to
CmsAuthenticatedData (Batch 15c):

• Class summary — streaming MAC-protected workflow, single-recipient constraint, and call-order note.
• Remarks — lazy content draining, MAC availability after EOF, stream disposal, buffering guidance,
  and a C# usage example including MAC comparison.
• Constructors — byte array and stream overloads; ArgumentNullException and CmsException on the
  stream constructor.
• Properties and accessors — MAC algorithm, originator information, recipient store, MAC value,
  and authenticated/unauthenticated attribute tables.

Legacy /** block comments converted to XML.

Key Accomplishments

• Streaming authenticated-data discoverability: IDE tooltips now cover the parser surface.
• Accurate exception contracts: documented only where the constructor validates or parses input.
• Focused scope: single file; no behavioural or signature changes.
• Documentation quality: all new or modified XML documentation lines are at most 120 characters.

Verification

• Build Status: dotnet build crypto/src/BouncyCastle.Crypto.csproj -c Release — 0 errors, no new warnings.
• Scope: Documentation-only; no behavioural or signature changes.

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.