Go SDK: Upgrade MCP SDK and remove vendored copy

[jeongukjae]

Update the Go interceptor SDK to use github.com/modelcontextprotocol/go-sdk v1.7.0 custom method APIs and remove the vendored Go SDK copy. This shouldn't update the behaviours, but addding following functions.

Changed public/user-facing interfaces:
extension.Extension.Install now returns an error:

// before
ext.Install(mcpServer)

// after
if err := ext.Install(mcpServer); err != nil {
	return err
}

New helper added:

extension.RegisterSendingMethods(client *mcp.Client) error

Motivation and Context

Pick up MCP Go SDK 1.7.0. This provides upstream custom method support, so the local vendored SDK copy is no longer needed.

How Has This Been Tested?

• go test -v ./...

Breaking Changes

if err := ext.Install(mcpServer); err != nil {
    return err
}

The Go SDK module now requires Go 1.25 via github.com/modelcontextprotocol/go-sdk v1.7.0.

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

LocalChain now registers interceptor custom sending methods internally. Manual remote chain setup should call extension.RegisterSendingMethods(client) before connecting the MCP client session used with chain.AddMCPServer.