Make `McpClientFactory` accept an `IClientTransport` directly instead of `McpServerConfig`

[eiriktsarpalis]

each transport implementation should define its own options object if necessary

That sounds reasonable.

Originally posted by @stephentoub in #181

Spinning off this conversation into a new issue. What I have in mind roughly is change the McpClientFactory signature to be the following:

public static class McpClientFactory
{
    public static async Task<IMcpClient> CreateAsync(
        IClientTransport transport,
        McpClientOptions? clientOptions = null,
        ILoggerFactory? loggerFactory = null,
        CancellationToken cancellationToken = default);
}

Then exposing bespoke configuration options for individual transports

public record StdioClientTransportOptions
{
     public string Executable { get; init; }
     public IReadOnlyList<string> Arguments { get; init; }
     /* etc etc */
}

public class StdioClientTransport : IClientTransport
{
     public StdioClientTransport(StdioClientTransportOptions options, ....); // No McpServerConfig argument anymore
}

This seems perfectly doable, the only blocker in my view is that ITransport instances are currently stateful. For this to work best we need to be able to offload all their state in session objects created by the client factory. cc @halter73

[eiriktsarpalis]

Fixed by #230