Fix duplicate instances on toast click when IPC forward times out

[Gabriel Dufresne (GabrielDuf)]

This pull request refactors and improves the single-instance handling logic in SingleInstanceRedirector.cs to make inter-process communication via named pipes more robust and responsive. The main improvements are around error handling, non-blocking connection management, and timeouts for both reading and forwarding arguments between instances.

Named pipe connection handling improvements:

• The listener now uses NamedPipeServerStream.MaxAllowedServerInstances and asynchronous options, allowing multiple incoming connections to be handled without blocking the main thread. Each client connection is processed off-thread, so a slow or stuck client cannot prevent new connections. (src/UniGetUI.Avalonia/Infrastructure/SingleInstanceRedirector.cs)
• Added a new HandleConnection method that reads pipe input asynchronously with a timeout (ReadTimeout), preventing clients that never send EOF from blocking the server. Errors are logged without crashing the listener. (src/UniGetUI.Avalonia/Infrastructure/SingleInstanceRedirector.cs)

Timeouts and retry logic:

• Introduced ForwardBudget and ReadTimeout constants to bound how long the process will attempt to forward arguments to the first instance and how long it will wait for pipe reads, respectively. (src/UniGetUI.Avalonia/Infrastructure/SingleInstanceRedirector.cs)
• The TryForwardToFirstInstance method now retries connecting and sending arguments to the first instance until the ForwardBudget expires, logging the last error if unsuccessful. (src/UniGetUI.Avalonia/Infrastructure/SingleInstanceRedirector.cs)

[Copilot]

Pull request overview

Improves single-instance IPC resilience for Avalonia launches.

Changes:

• Handles concurrent named-pipe connections asynchronously.
• Adds read and forwarding timeouts with retry logic.
• Prevents stalled clients from blocking subsequent activations.

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