Manual execution of field-level access control on retrieved documents

[Fitch24]

Introduce an API to manually apply field-level access control to already retrieved documents. This would be useful in custom endpoints where documents are fetched with overrideAccess: true, modified, and then need to be sanitized before returning to the client.

Currently, developers must either manually strip restricted fields (error-prone and tightly coupled to access configs) or re-fetch documents with overrideAccess: false, which negatively impacts performance. A built-in utility to reapply field access rules would improve safety, maintainability, and efficiency.