Break apart metrics into their own module (#335)

Signed-off-by: José Ulises Niño Rivera <junr03@users.noreply.github.com>

crates/llm_gateway/src/metrics.rs

@@ -0,0 +1,28 @@
+use common::stats::{Counter, Gauge, Histogram};
+
+#[derive(Copy, Clone, Debug)]
+pub struct Metrics {
+    pub active_http_calls: Gauge,
+    pub ratelimited_rq: Counter,
+    pub time_to_first_token: Histogram,
+    pub time_per_output_token: Histogram,
+    pub tokens_per_second: Histogram,
+    pub request_latency: Histogram,
+    pub output_sequence_length: Histogram,
+    pub input_sequence_length: Histogram,
+}
+
+impl Metrics {
+    pub fn new() -> Metrics {
+        Metrics {
+            active_http_calls: Gauge::new(String::from("active_http_calls")),
+            ratelimited_rq: Counter::new(String::from("ratelimited_rq")),
+            time_to_first_token: Histogram::new(String::from("time_to_first_token")),
+            time_per_output_token: Histogram::new(String::from("time_per_output_token")),
+            tokens_per_second: Histogram::new(String::from("tokens_per_second")),
+            request_latency: Histogram::new(String::from("request_latency")),
+            output_sequence_length: Histogram::new(String::from("output_sequence_length")),
+            input_sequence_length: Histogram::new(String::from("input_sequence_length")),
+        }
+    }
+}