Add next page token to PagedResult

In many cases a token for the next page is used, but neither PagedResult or PagedInfo includes this.
This could be solved by adding a string property to either PagedResult or PagedInfo.

I'm glad to do a PR with proposed changes.

Start by locating the PagedResult and PagedInfo definitions and reading how paged results are constructed and consumed. Determine which type should carry the string next-page token, then verify that the selected type exposes it wherever pagination results are returned. Done means callers can provide and retrieve the token without breaking existing result usage.

Written by the indexing model from the issue text.