docs: add XML documentation for Classic McEliece key parameters (Batch 13b-3)

[KonradSop]

Description

Adds XML documentation to the Classic McEliece KEM parameter and key classes (all previously undocumented):

• CmceParameters — class summary (including what the f "fast" variants mean), all ten mceliece* instances, and the public properties (Name, M, N, T, Mu, Nu, DefaultKeySize).
• CmceKeyParameters — base class summary, Parameters.
• CmceKeyGenerationParameters — class summary, constructor, Parameters.
• CmcePublicKeyParameters — class summary, constructor, GetPublicKey, GetEncoded.
• CmcePrivateKeyParameters — class summary, both constructors (raw and component-field), GetPrivateKey, ReconstructPublicKey, GetEncoded.

PQC reference style preserved — documentation only, no code changes.

Key Accomplishments

• Classic McEliece discoverability: IDE tooltips now cover the full public parameter/key surface (0 → docs across 5 files), including the r3 vs f variant distinction.
• Consistent style: matches the merged ML-KEM/ML-DSA parameter docs (Batch 5/9).

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.