Populate request peer metadata across server adapters

### Summary

`livery_req:peer/1` is part of the public request model, but the H1, H2, and H3 server adapters currently return `undefined` from `peer_info/1`. This prevents handlers and middleware from safely implementing trusted-proxy processing, client-IP logging, and source-aware access controls.

### Requested behavior

Populate `peer` with `{inet:ip_address(), inet:port_number()}` for accepted server connections across H1, H2, and H3. TLS metadata can remain separate in the existing `tls` field.

It would be helpful to define what happens when peer lookup fails (presumably `undefined`) and add adapter-level tests for IPv4 and IPv6.

The underlying H1/H2 libraries may need a supported connection-info accessor so Livery does not inspect private process state.

Start at the H1, H2, and H3 server adapters and their peer_info/1 implementations, then inspect the underlying H1/H2 connection-info accessors. Add adapter-level IPv4 and IPv6 tests, define the lookup-failure result as described, and verify accepted connections populate peer without changing tls.

Written by the indexing model from the issue text.