fix(server): install timer for HTTP/2 connections

[mindrunner]

Summary

• Install TokioTimer on the server HTTP/2 builder used by accepted connections.
• Install TokioTimer on the low-level serve and serve_with_graceful_shutdown helpers.

Context

Hyper 1.x requires an explicit timer for HTTP/2 keep-alive / timeout handling. jsonrpsee exposes server keep-alive configuration via ServerConfigBuilder::set_keep_alive, but the underlying hyper_util::server::conn::auto::Builder is currently created with only TokioExecutor.

That means a server configured with HTTP/2 keep-alive can panic at runtime when an HTTP/2 connection constructs hyper's ping channel:

You must supply a timer.

This mirrors the timer setup tonic added for its hyper-backed server path.