Manual server updates

[jigar-f]

This pull request introduces several improvements and refactors related to server reachability warnings and server list updates in the Lantern app. Key changes include a new reusable warning icon widget, streamlined logic for updating available servers after URL-test events, and improved UI logic for displaying server lists.

UI/UX Improvements:

• Added a new ServerReachabilityWarningIcon widget for consistent display of server reachability warnings, replacing prior ad-hoc implementations. This widget provides an info icon with tooltip and accessibility support (lib/core/widgets/server_reachability_warning_icon.dart, lib/core/widgets/server_reachability_warning_icon.dartR1-R27).
• Updated server selection UI to use the new warning icon and improved the logic for displaying reachable and unavailable server sections, especially for Pro users (lib/features/vpn/location_setting.dart, [1]; lib/features/vpn/server_selection.dart, [2] [3] [4] [5] [6].

Codebase Simplification & Refactoring:

• Removed the now-obsolete server_reachability.dart file and its associated logic, consolidating warning icon usage into the new widget (lib/features/vpn/server_reachability.dart, lib/features/vpn/server_reachability.dartL1-L53).
• Cleaned up AvailableServersNotifier by removing unused throttle/delay logic and the refreshAvailableServersAfterProbeSettle method, simplifying server refresh operations (lib/features/vpn/provider/available_servers_notifier.dart, [1] [2].

Event Handling and Data Refresh:

• Added support for a new url-test event type in both the backend (Go) and Flutter layers, ensuring that the UI always reflects the latest server latency data after URL-test runs (lantern-core/core.go, [1] [2] [3]; lib/features/home/provider/app_event_notifier.dart, [4].
• Updated the server selection screen to always use the simplified forceFetchAvailableServers method after probe events, ensuring up-to-date server information (lib/features/vpn/server_selection.dart, lib/features/vpn/server_selection.dartL44-R43).

Dependency Updates:

• Updated several Go dependencies to newer versions, including broflake, lantern-box, and sing-tun, and removed some unused or old pion and nats dependencies (go.mod, [1] [2] [3] [4].

These changes collectively improve the reliability, maintainability, and user experience of server selection and reachability warnings in the app.

[jigar-f]

Depends on getlantern/radiance#530

[Copilot]

Pull request overview

This PR refactors how server reachability warnings are displayed in the Flutter UI (moving from ad-hoc helpers to a reusable widget), and updates the app’s server-refresh behavior to react to additional backend events (including a new url-test completion event), alongside some dependency churn in the Go module.

Changes:

• Introduces ServerReachabilityWarningIcon and replaces prior reachability subtitle/icon helpers across server-selection UIs.
• Simplifies available-servers refreshing by consistently using forceFetchAvailableServers() after relevant events (including new url-test).
• Adds a Go-side URL-test event listener that forwards url-test events to Flutter.

Reviewed changes

Copilot reviewed 10 out of 11 changed files in this pull request and generated 6 comments.

Show a summary per file

File	Description
lib/features/vpn/single_city_server_view.dart	Replaces reachability subtitle/icon helpers with a type subtitle and the new warning icon widget.
lib/features/vpn/server_selection.dart	Updates selection UI to use the new icon/widget and changes refresh behavior after probe-related flows.
lib/features/vpn/server_reachability.dart	Removes obsolete reachability subtitle/icon helper utilities.
lib/features/vpn/provider/available_servers_notifier.dart	Removes probe-settle refresh logic and relies on forceFetchAvailableServers().
lib/features/vpn/location_setting.dart	Switches warning icon usage to the new reusable widget.
lib/features/home/provider/app_event_notifier.dart	Adds handling for url-test events to refresh available servers.
lib/core/widgets/server_reachability_warning_icon.dart	Adds new reusable warning/info icon widget with tooltip + semantics label.
lib/core/common/common.dart	Exports the new widget via common exports.
lantern-core/core.go	Adds EventTypeURLTest and a listener that forwards URL-test completion events to Flutter.
go.mod	Updates module replacements/dependency versions (notably enabling a local radiance replace).
go.sum	Updates checksums to match Go dependency changes.

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[jigar-f]

@atavism, all comments addressed.