Add URL-type elicitation schema support allowing servers to request URL
input from users during tool execution. This enables out-of-band
interactions like payment processing or API key entry.

Breaking changes:

- `ElicitRequest` changed from a `record` to an `interface`.
- The original `ElicitRequest` record was renamed to `ElicitFormRequest`.
- `McpClient` builder `elicitation()` methods now accept `ElicitFormRequest` instead of `ElicitRequest`.

New APIs:

- `ElicitUrlRequest` record for URL-mode elicitation.
- `urlElicitation()` builder methods in `McpClient`.
- `elicitationCompleteConsumer()` and `elicitationCompleteConsumers()` builder methods in `McpClient`.
- `sendElicitationComplete()` methods in `McpAsyncServer` and `McpSyncServer`.
- `McpError.URL_ELICITATION_REQUIRED` and `McpSchema.ErrorCodes.URL_ELICITATION_REQUIRED`.
- `ElicitationCompleteNotification` record and `METHOD_NOTIFICATION_ELICITATION_COMPLETE` constant.

Co-authored-by: Daniel Garnier-Moiroux <git@garnier.wf>
Co-authored-by: Sainath Reddy Bobbala <bsnr@amazon.com>