Add SHARE_CODE resource support for session creation and retrieval

[Copilot]

Implements support for requesting and retrieving SHARE_CODE resources in DocScan sessions per SDK-2752 requirements.

Session Creation

Added RequiredShareCode model and builder for specifying share code requirements:

var session = new SessionSpecificationBuilder()
    .WithRequiredShareCode(
        new RequiredShareCodeBuilder()
            .WithIssuer("example_issuer")
            .WithScheme("example_scheme")
            .Build())
    .Build();

Serializes to required_share_codes array in session creation requests. No SDK-level validation applied per spec.

Session Retrieval

• ShareCodeResourceResponse: Handles share_codes array in resources with fields: id, source, created_at, last_updated, lookup_profile, returned_profile, id_photo, file
• VerifyShareCodeTaskResponse: Supports VERIFY_SHARE_CODE_TASK type with generated_media field
• MediaContainerResponse: Reusable wrapper for nested media objects
• GetSessionResult.GetShareCodes(): Convenience method following existing resource accessor pattern

Technical Details

• Extended ResourceContainer with ShareCodes property
• Added VERIFY_SHARE_CODE_TASK constant and JsonSubTypes mapping
• All media containers use existing MediaResponse model
• Follows established internal setter pattern for response models

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