paniced when rawMessage is nil in ParseCallToolResult #207
Description
In code https://github.com/mark3labs/mcp-go/blob/main/mcp/utils.go#L502
It doesn't check if the rawMessage is null. In some special scenario，the result in the response of tool call result is empty, cause it paniced.
Same issue occurred in ParseGetPromptResult, ParseResourceContents, ParseReadResourceResult.