Add Elysia server support to grafserv

[zuohuadong]

Summary

This PR adds support for the Elysia web framework to grafserv, enabling developers to use Elysia as a server option for their GraphQL APIs.

Changes

• New ElysiaGrafserv class: Implements full integration with Elysia framework
• GraphQL support: Complete GraphQL query and mutation handling
• GraphiQL interface: Built-in GraphiQL IDE support
• WebSocket support: GraphQL subscriptions via graphql-ws protocol
• Event stream support: Server-sent events for watch mode
• Package configuration: Added Elysia as an optional peer dependency with proper export paths

Implementation details

The implementation follows the same patterns as existing server integrations (Koa, Express, Fastify, Hono, etc.) and includes:

• Request digest extraction from Elysia context
• WebSocket handler for GraphQL subscriptions
• Event handlers for GraphQL, GraphiQL, and static assets
• Proper header and status code handling
• Stream support for event-stream responses

Test plan

• Verify GraphQL queries work correctly with Elysia server
• Test GraphiQL interface loads and functions properly
• Confirm WebSocket subscriptions work as expected
• Validate event stream functionality for watch mode
• Check that the package builds without errors
• Ensure TypeScript types are properly exported

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[benjie]

Thank you for your pull request. Since I am not familiar with Elysia I will not be merging this before the 5.0.0 release, and with the winter holidays coming up it might be 2-3 months before I get around to reviewing it. Rest assured that it is on my TODO list to familiarize myself with this.

In the mean time, have you considered releasing this as its own grafserv-elysia module?