docs: add InferDI (dependency injection) example

[maxrendel]

What

Adds a new example — InferDI (Dependency Injection) — under
Examples → 3rd-party Middleware, with a matching sidebar link.

The guide walks through using InferDI's official @inferdi/hono
request-scope middleware in a Hono app:

• building a typed DI container with singleton / scoped / transient lifetimes
• wiring inferdiHono and typing the context via InferdiHonoEnv
• hydrating the per-request scope with setupScope
• resolving services in handlers through c.var.di
• the middleware options table and streaming (skipInferdiDispose)

Why

Implements the proposal agreed in #869.

Notes

• All code samples are checked against the published @inferdi/hono API.
• Formatted with the repo's Prettier config.

Closes #869

[yusukebe]

LGTM!

[yusukebe]

Thank you @maxrendel !