feat!: capabilities for tasks, elicitation (#732)

closes #544 

Replaces opaque `JsonObject?` modelling of `elicitation` with a typed
`ClientCapabilities.Elicitation` (`form`, `url`), and adds the new
`tasks` capability on both `ClientCapabilities` and `ServerCapabilities`
(with `list`, `cancel`, per-request-type augmentation). Wires capability
assertions for `tasks/*` methods and `notifications/tasks/status` into
`Client` and `ServerSession`

## How Has This Been Tested?
unit tests 

## Breaking Changes
yes
now elicitation is a specific class in capabilities 

## Types of changes
- [ ] Bug fix (non-breaking change which fixes an issue)
- [x] New feature (non-breaking change which adds functionality)
- [x] Breaking change (fix or feature that would cause existing
functionality to change)
- [ ] Documentation update

## Checklist
- [x] I have read the [MCP
Documentation](https://modelcontextprotocol.io)
- [x] My code follows the repository's style guidelines
- [x] New and existing tests pass locally
- [x] I have added appropriate error handling
- [x] I have added or updated documentation as needed

integration-test/src/commonTest/kotlin/io/modelcontextprotocol/kotlin/sdk/client/ClientTest.kt

@@ -1058,7 +1058,7 @@ class ClientTest {
             Implementation(name = "test client", version = "1.0"),
             ClientOptions(
                 capabilities = ClientCapabilities(
-                    elicitation = EmptyJsonObject,
+                    elicitation = ClientCapabilities.Elicitation(),
                 ),
             ),
         )
@@ -1270,7 +1270,7 @@ class ClientTest {
     ): Pair<Client, ServerSession> = kotlinx.coroutines.coroutineScope {
         val client = Client(
             Implementation(name = "test client", version = "1.0"),
-            ClientOptions(capabilities = ClientCapabilities(elicitation = EmptyJsonObject)),
+            ClientOptions(capabilities = ClientCapabilities(elicitation = ClientCapabilities.Elicitation())),
         )
         client.setElicitationHandler(handler)