feat: add PseudoTransport for in-process MCP client-server communication

[pluveto]

Add PseudoTransport class for in-process MCP client-server communication.

Motivation and Context

This change introduces a PseudoTransport implementation that allows an MCP client to communicate directly with an McpServer instance within the same process, bypassing network or stdio layers.

How Has This Been Tested?

• Used in local unit and integration tests to verify client-server interactions without network dependencies.
• Tested scenarios include message exchange, error propagation, connection lifecycle (start, send, close), and handler registration.
• Confirmed compatibility with existing MCP client and server APIs.

Breaking Changes

No breaking changes.
This is a new feature and does not affect existing APIs or configurations.

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

• The PseudoTransport class implements the Transport interface and can be used as a drop-in replacement for network transports in test or embedded environments.
• Server lifecycle management remains external to the transport, allowing flexible ownership patterns.
• All message delivery is asynchronous to simulate realistic client-server behavior.
• No external dependencies added.