Compile-time logging_for for applications with a hand-written Hooks impl #504

Summary

An application that implements Hooks by hand has no compile-time way to return the manifest's logging configuration from Hooks::logging_for. Only app! bakes it.

Behavior today

• app! generates logging_for from [adapters.*.logging] at compile time (crates/edgezero-macros/src/app.rs, build_logging_tokens).
• app! also generates the routes from manifest triggers. An application whose routes are not manifest triggers therefore writes its own Hooks impl, as Trusted Server does on all four adapters, and loses the baked table. Its only options are to parse edgezero.toml at runtime with ManifestLoader::load_from_str, or to copy the values into code.
• On Fastly, the managed setup calls logging_for before every callback. A non-reusable instance serves one request, so a runtime parse happens on every request, health checks included.

Acceptance criteria

• A hand-written Hooks impl can return the manifest's logging configuration for an adapter with no runtime parse and no copied values.
• The result equals what app! generates for the same manifest.
• The adapter guides document it.

Related

• Trusted Server parses the manifest per instance today (Cut Trusted Server over to EdgeZero PR 275 trusted-server#1506, Fastly TrustedServerApp::logging_for), and its follow-up waits on this.
• Part of Platform capabilities for server-side identity on every adapter #468. Follow-up, not blocking.