feat(McpSchema): Add constructor to CallToolResult with one String entry

[denniskawurek]

Adds a new constructor to CallToolResult which allows passing just a String.
The string argument is mapped to a List with just one TextContent element and makes the usage of creating a CallToolResult easier.

Motivation and Context

The Javadoc for the usage of CallToolResult is diverging from the implementation at serveral places.

As an example McpServer.java has the following example:

McpServer.sync(transportProvider)
 .serverInfo("my-server", "1.0.0")
 .tool(new Tool("calculator", "Performs calculations", schema),
  (exchange, args) -> new CallToolResult("Result: " + calculate(args)))
 .build();

But currently the CallToolResult expects different arguments and should be:

CallToolResult(
 List.of(
  new TextContent("Result: " + calculate(expr))
 ),
 false
)

As this can be confusing for new users of the SDK, I thought first that the documentation should be changed.

But on the other hand it's nice to have an easy way to create a CallToolResult with just one String entry.
This would enhance the readability of a codebase and make the usage easier.

This change enables the usage by adding an additional constructor to CallToolResult.

How Has This Been Tested?

Tested it only manually. I can add (Unit) tests if wanted.

Breaking Changes

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Documentation update

Checklist

• I have read the MCP Documentation
• My code follows the repository's style guidelines
• New and existing tests pass locally
• I have added appropriate error handling
• I have added or updated documentation as needed

Additional context

[He-Pin]

how about another success and failed one?

[tzolov]

Thanks you @denniskawurek ! Will review it over the weekend
It's been a very heckling week me.

[tzolov]

Thank you @denniskawurek,
I did some additional, usability, improvements to the CallToolResult and CallToolRequest.
Rebased, extended and merged at 8d5872f

[denniskawurek]

@tzolov perfect, thanks taking care of the PR and enhancing it!