Fix socket leak (CLOSE_WAIT) in NetworkTransport when reconnection is disabled - #283

Thanks @skirrellyjones, this is a real leak and the iMCP numbers are convincing. The change in the generic
catch is the one that fixes it. Three small things:

1. The NWError branch can't be reached. receiveData() wraps every NWError in
   MCPError.transportError (line ~765), so catch let error as NWError never matches. Errors and graceful
   peer closes (MCPError.connectionClosed) all go through the generic catch, which is where your second
   change does the work. Fine to keep the first one for safety, but worth knowing.
2. One more exit leaks. The break after repeated empty reads when connection.state != .ready
   (line ~613) leaves the connection uncancelled and never finishes the message stream, so receive()
   callers hang. Could you cancel and messageContinuation.finish(throwing: MCPError.connectionClosed) there
   too (when not reconnecting)?
3. A regression test. This fails on main and passes with your change:

   @Test("Receive failure with reconnection disabled cancels the connection")
   func receiveFailureCancelsConnection() async throws {
       let mockConnection = MockNetworkConnection()
       let transport = NetworkTransport(
           mockConnection, heartbeatConfig: .disabled, reconnectionConfig: .disabled)
       try await transport.connect()
       let stream = await transport.receive()
       mockConnection.simulateFailure(error: NWError.posix(.ECONNRESET))
       var streamError: Swift.Error?
       do { for try await _ in stream {} } catch { streamError = error }
       #expect(streamError != nil)
       var cancelled = false
       for _ in 0..<50 {
           if case .cancelled = mockConnection.state { cancelled = true; break }
           try await Task.sleep(for: .milliseconds(20))
       }
       #expect(cancelled)
       await transport.disconnect()
   }

Also, please rebase onto main to pick up the CI fix (#306). Happy to merge after that.