fix(ui_firestore): keep loaded pages while the next page is only in cache

[demolaf]

Fixes #238.

Stops FirestoreQueryBuilder from rendering a partial cache snapshot while fetching the next page, which shrank the list, set hasMore to false and reset the scroll position on web.

Changes

• While a next page loads, ignore cache-only snapshots that drop more than one doc from the screen until the server responds. Snapshots that don't shrink the list, or drop one doc as a local delete does, render as before, so offline pagination still reaches the end.
• Listen with metadata changes while waiting, so a server result identical to the cache still ends the fetch. Metadata-only events are still not rendered unless includeMetadataChanges is set.
• Clear both isFetching and isFetchingMore on every event and error, so a query change mid-fetch no longer leaves fetchMore stuck.
• Add widget tests for each case.

[gemini-code-assist]

Code Review

This pull request upgrades the google_sign_in dependency to version 7.1.0 across packages and updates the Google authentication provider and buttons to support the new API, including adding support for serverClientId and handling separate authentication and authorization steps. Additionally, it improves FirestoreQueryBuilder to prevent list shrinking and scroll resetting by keeping current pages until the server responds when a new listener emits from the local cache. Feedback suggests wrapping the initialization and sign-out process in a try-catch block to prevent potential exceptions from blocking the main logout flow.

[demolaf]

/gemini review

[gemini-code-assist]

Code Review

This pull request improves the FirestoreQueryBuilder in firebase_ui_firestore to prevent list shrinking and scroll position resets when fetching subsequent pages. It retains current documents until the server responds or the user writes locally, ignoring smaller cached results while waiting for the server. It also optimizes the handling of metadata-only events and simplifies state updates on errors. Additionally, comprehensive widget tests have been added to verify these behaviors, and mock classes in tests have been updated accordingly. There are no review comments, and I have no further feedback to provide.

[russellwheatley]

One thing on the shrink check.