Deprecate the SelectServerOptions interface, with internalization planned for the next major version.

Rationale:

• SelectServerOptions is marked @public in src/sdam/topology.ts but is not used by any public API, so it is public by accident rather than by design.
• Making it internal is tracked in NODE-7342, whose stated dependency is that the type must be deprecated first.
• Deprecating it in a 7.x minor gives consumers a release of warning before the type stops being exported.

Scope: add an @deprecated tag to SelectServerOptions, note it in the API docs and changelog, and schedule internalization for the next major.

This must ship in a 7.x minor before the V8 branch is cut, otherwise NODE-7342 cannot be included in V8.

This is standalone deprecation work and does not belong inside any feature ticket.