`createMcpHonoApp` should support generics for Env (Bindings and Variables)

[yokonao]

NOTE: This issue is a feedback for v2 alpha.

https://github.com/modelcontextprotocol/typescript-sdk/blob/%40modelcontextprotocol/hono%402.0.0-alpha.2/packages/middleware/hono/src/hono.ts#L44

Currently, createMcpHonoApp returns a plain Hono instance with BlankEnv({}).

This makes it difficult to access typed environment variables (like c.env.DB in Cloudflare D1) within MCP handlers without resorting to unsafe type casting.

It would be great if we could pass Env types like:

const app = createMcpHonoApp<Env>();

[dagangtj]

I'd like to work on this issue. Will implement generic type support for to allow custom Env types.