SSE transport doesn't handle absolute URI endpoints

[hiranya911]

Describe the bug
Some MCP servers respond with absolute URIs in the endpoint event:

event: endpoint
data: https://www.mcp.run/api/mcp/sse?sid=123456

The SseClientTransport assumes that the endpoint is always going to be relative URI, which doesn't work for cases like the above.

kotlin-sdk/src/commonMain/kotlin/io/modelcontextprotocol/kotlin/sdk/client/SSEClientTransport.kt

Lines 82 to 83 in 63a50c1

	// check url correctness
	val maybeEndpoint = Url(baseUrl + eventData)

Ideally the client should check if the endpoint is an absolute URI, and if so use that without adding any prefixes.