Simplify attribution of elicitation to a tool call

Currently one needs to do something like:

server.tool('elicit_inputs', 'Elicitation test tool', {}, async (_request, extra) => {
  const result = await server.server.elicitInput(
    {
      message: 'Please provide inputs for the following fields:',
      requestedSchema: ...
    },
    {
      relatedRequestId: extra.requestId,
    },
  )
  ...
})

I think we should add a zod-typed elicitInput method to tool callback extras + McpServer that then calls the low-level server's elicitInput (related to https://github.com/modelcontextprotocol/typescript-sdk/issues/662):

// Tool-related elicitation:
server.tool('elicit_inputs', 'Elicitation test tool', {}, async (_request, extra) => {
  const result = await extra.elicitInput(
      'Please provide inputs for the following fields:',
      z.object(...))
  ...
})

// Non-tool-related elicitation
setInterval(async () => {
  const {action, content} = await server.elicitInput('It has been an hour. Wanna post something?', z.object(....), {timeout: 30_000});
  if (action == 'accept) ...
}, 3_600_000);

// Note: some connections might need help to stay alive.
setInterval(() => server.ping(), 5_000);