feat: add routing hook and scope["route"] for observability instrumentation

[thanhlim]

Summary

This PR adds two related features to improve observability instrumentation compatibility.

Relates to #2036

1. Set scope["route"] for OpenTelemetry/ASGI instrumentation

OpenTelemetry's ASGI middleware reads scope["route"].path to populate the http.route span attribute. Without this, APM tools like NewRelic show transaction names with actual path values (e.g., /users/12345) instead of templated routes (e.g., /users/{user_id}), making it impossible to aggregate metrics properly.

This change sets scope["route"] to a SimpleNamespace(path=full_route_path) after routing resolution, where full_route_path includes the API base path and the OpenAPI path template.

2. Add after_routing_resolution hook mechanism

Provides a general-purpose hook that runs after Connexion determines which operation handles a request, but before the operation is invoked. This enables:

• Observability: Set span attributes, update trace names (OTEL, Datadog, etc.)
• Logging: Log route information with structured context
• Metrics: Record routing metrics or counters
• Auditing: Track which operations are called

Usage

from connexion.middleware.routing import RoutingOperation

def my_hook(route_path: str, operation_id: str | None, scope: dict) -> None:
    # route_path: "/v1/users/{user_id}" (OpenAPI template)
    # operation_id: "get_user" (from OpenAPI spec)
    # scope: ASGI scope dict
    print(f"Routing {scope['method']} to {route_path}")

RoutingOperation.after_routing_resolution(my_hook)

Hook errors are caught and logged at DEBUG level to avoid breaking request processing.

Test Plan

• Added RoutePathMiddleware test to verify scope["route"].path is set correctly
• Added TestRoutingHooks class with tests for:
  • Hook receives correct route_path, operation_id, and scope
  • Multiple hooks are all invoked
  • Hook errors don't break request processing