Remove SchemaValidator

[Nyholm]

Motivation and Context

This is more of an issue or question.

I noticed the SchemaValidator. It is never used and not documented. Do we really need it in the sdk?

How Has This Been Tested?

Breaking Changes

Yes, removing classes is a breaking change

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

[chr-hertel]

Oh, i guess that's my bad by merging the SDKs, it was used before to validate incoming argument collection on a tool call actually meets the input schema of that registered tool:

https://github.com/php-mcp/server/blob/d2c583302c4d08dea887c7cbae49c767b0ce75b9/src/Dispatcher.php#L164-L184

So would live here now:

php-sdk/src/Server/Handler/Request/CallToolHandler.php

Lines 61 to 66 in 3b31954

	$reference = $this->registry->getTool($toolName);
	$arguments['_session'] = $session;
	$arguments['_request'] = $request;
	$result = $this->referenceHandler->handle($reference, $arguments);

I guess there's still value in having that and integrating it again, don't you think?