Fix race conditions and delayed connections

[atdrendel]

• Fix race conditions where a Task was created and thus started before the Task it was replacing had been cancelled
• Speed up PhoenixSocket.connect() by correctly resetting reconnection state in both disconnect() and connect()

[Copilot]

Pull request overview

This PR addresses reconnection/flush task race conditions in the Phoenix client and reduces delayed reconnect behavior by ensuring prior tasks/continuations are properly cancelled before starting replacements.

Changes:

• Add PushBuffer.cancelAwaitingContinuation() and cancel prior timeout tasks when updating the next timeout.
• Fix PhoenixSocket task replacement races (flush/listen/heartbeat/reconnect) and reset reconnection state when connecting/disconnecting during a reconnect loop.
• Add regression tests for cancelling an awaiting iterator and for reconnect-loop behavior around disconnect()/connect().

Reviewed changes

Copilot reviewed 6 out of 6 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
Tests/PhoenixTests/PushBufferTests.swift	Adds tests for cancelling an awaiting iterator and ensuring a new iterator can proceed afterward.
Tests/PhoenixTests/PhoenixSocketTests.swift	Adds tests ensuring disconnect() stops reconnect loops and connect() after disconnect during reconnect has no backoff.
Sources/Phoenix/PushBuffer.swift	Adds continuation cancellation helper and fixes timeout task replacement by cancelling the previous task.
Sources/Phoenix/PhoenixSocket.swift	Cancels/replaces stored tasks safely, resets reconnect state on connect/disconnect, and improves cancellation handling in doConnect().
Package.swift	Raises minimum supported platform versions.
.github/workflows/ci.yml	Updates CI runner and hard-pins an Xcode app bundle path.

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