TLS not enabling for dynamic fastly backends

[ChristianPavilonis]

Problem:
The ensure_backend function in the Fastly adapter has several issues that can cause TLS connections to fail or behave unexpectedly:

1. Missing default ports — When a URI has no explicit port, the backend target is set to just the hostname (e.g., example.com) instead of example.com:443 or example.com:80. This can cause connection issues.
2. Incomplete SSL configuration — The original code only calls enable_ssl() but omits sni_hostname() and check_certificate(), which are required for proper TLS with SNI and certificate validation.
3. No timeouts — The backend has no timeout configuration, relying on unknown Fastly defaults.
4. Fragile error handling — On builder.finish() failure, the code retries with a second builder without override_host, which may work by accident but doesn't properly handle the "backend name already exists" case.
5. Hash-based naming — Backend names like edgezero-dynamic-a1b2c3d4... are hard to debug in logs.
   Expected behavior:
   Dynamic backends should have explicit ports, proper TLS configuration with SNI/certificate validation, sensible timeouts, and clear error handling for the "name already in use" case.