Evaluate lazy initialization for Sodium size constants to avoid type-initialization lockout

[MariusStorhaug]

During PR #45 review, a valid concern was raised about static field initialization in PSModule/Sodium/Sodium.cs: PublicKeyBytes, SecretKeyBytes, SealBytes, and SeedBytes are populated via native P/Invoke at type initialization time. If libsodium cannot be loaded, type initialization can fail and poison the type for the process lifetime, reducing recoverability and masking diagnostics.

This follow-up should evaluate a lazy initialization approach (for example Lazy or deferred first-use resolution) so native load failures are surfaced with clearer diagnostics and can be retried in-session after remediation.

Context:

• Triggered by review threads: r3254554854 and r3254586271
• PR reference: 🩹 [Patch]: Secret crypto operations now fail fast on invalid input with lower per-call overhead #45