HTTPClient: verbose logs for request IDs (#3320)

See https://github.com/RevenueCat/khepri/pull/6798.
This can help debug issues as it helps us cross-reference requests on
our end.

### Changes:
- Logging `X-Request-ID` and `X-Amzn-Trace-ID` headers if present (only
in verbose mode)
- Logging these even for failed requests
- Also logging `request_handled_by_load_shedder` for failed requests
- To accomplish that. `HTTPURLResponse` now conforms to our
`HTTPResponseType`, this allows us to extract headers in an uniform way

### Example:
```
[network] DEBUG: ℹ️ API request completed: GET '/v1/subscribers/$RCAnonymousID%3Ad9dc4f3b33054cf28c0f2ec9da0f48d5' (304)
Request-ID: 'be534c50-5231-403b-be2f-7c077861751d'; Amzn-Trace-ID: 'Root=1-6532c6ca-7ef80f961ec9c4145484df13'
```

Sources/Networking/HTTPClient/HTTPStatusCode.swift

@@ -101,13 +101,3 @@ extension HTTPStatusCode {
     }
 
 }
-
-extension URLResponse {
-
-    var httpStatusCode: HTTPStatusCode? {
-        guard let response = self as? HTTPURLResponse else { return nil }
-
-        return .init(rawValue: response.statusCode)
-    }
-
-}