[LubabaKhalid]

Built-in telemetry server routes are inserted before custom routes, so a custom route on the same path and method as a built-in one is silently ignored. This is easy to hit by accident, and a built-in route added in a later release can start shadowing an existing custom route without any warning.

This adds TelemetryServerRoute::collides_with_built_in_route, which returns true if the route collides with a built-in route for any of its methods. Services can call it at startup and fail or warn as they see fit:

for route in &custom_routes {
    if route.collides_with_built_in_route() {
        anyhow::bail!("telemetry route `{}` collides with a built-in route", route.path);
    }
}

The check builds the built-in routes for the enabled features and tries to insert the route into a copy of each method's router, so it follows the same conflict rules as the server itself, with and without telemetry-server-pattern-routing. The parameter escaping that Routes::set did inline moved into a small helper so both use the same path handling.

Testing

• New test covering collisions (GET /health, GET /metrics), the same path on a method the built-in route does not handle (POST /health), and a path with no built-in route.
• cargo test -p foundations --test telemetry_server with and without telemetry-server-pattern-routing.
• cargo clippy -p foundations --all-targets with the CI lint flags, for both feature sets.
• rustfmt --check --edition 2024.

Closes #200

[LubabaKhalid]

@TheJokr this adds the built-in route collision check you suggested. Could you take a look when you have a moment? Thanks!