Add an ElicitAsync<T> overload

[stephentoub]

Right now, we expose this overload for a server to elicit a user response:

csharp-sdk/src/ModelContextProtocol.Core/Server/McpServerExtensions.cs

Lines 223 to 224 in 3156818

	public static ValueTask<ElicitResult> ElicitAsync(
	this IMcpServer server, ElicitRequestParams request, CancellationToken cancellationToken = default)

public static ValueTask<ElicitResult> ElicitAsync(
        this IMcpServer server, ElicitRequestParams request, CancellationToken cancellationToken = default)

We could smooth this over with another overload something like:

public static ValueTask<ElicitResult<T?>> ElicitAsync<T>(
        this IMcpServer server, string message, JsonSerializerOptions? serializerOptions = null, CancellationToken cancellationToken = default) where T : class

where we use the T to create the request schema and then automatically deserialize the response if the user supplied the requested data.

(Elicitation, however, employs a very constrained subset of JSON schema, so this would only work with a subset of Ts.)

[mikekistler]

I like this idea -- it could eliminate some of the bulky code currently needed for Elicitation.

[mehrandvd]

@stephentoub I'd like to volunteer for this as my first contribution to MCP. Could you assign it to me?