feat(proxy): add request IDs, tracing spans, and observability hooks

Generate UUID v4 request IDs per request, create manual tracing spans
(Pingora types don't impl Debug), record Prometheus metrics for
detection decisions and request totals, and forward X-Request-Id to
both upstream requests and downstream responses.

Signed-off-by: Sienna Meridian Satterwhite <sienna@sunbeam.pt>

Cargo.toml

@@ -52,6 +52,9 @@ dns-lookup  = "2"
 # Prometheus metrics
 prometheus  = "0.13"
 
+# Request IDs
+uuid = { version = "1", features = ["v4"] }
+
 # Rustls crypto provider — must be installed before any TLS init
 rustls      = { version = "0.23", features = ["aws-lc-rs"] }