Add ASGI Request-Id correlation, add structlog LoggingMiddleware, overhaul all logging

- minor formatting details, type fixes.

backend/linkpulse/middleware.py

@@ -0,0 +1,51 @@
+import time
+from asgi_correlation_id import correlation_id
+import structlog
+
+from fastapi import FastAPI, Request, Response
+from starlette.middleware.base import BaseHTTPMiddleware
+
+
+
+class LoggingMiddleware(BaseHTTPMiddleware):
+    def __init__(self, app: FastAPI):
+        super().__init__(app)
+        self.access_logger = structlog.get_logger("api.access")
+
+    async def dispatch(self, request: Request, call_next) -> Response:
+        structlog.contextvars.clear_contextvars()
+
+        # These context vars will be added to all log entries emitted during the request
+        request_id = correlation_id.get()
+        structlog.contextvars.bind_contextvars(request_id=request_id)
+
+        start_time = time.perf_counter_ns()
+        # If the call_next raises an error, we still want to return our own 500 response,
+        # so we can add headers to it (process time, request ID...)
+        response = Response(status_code=500)
+        try:
+            response = await call_next(request)
+        except Exception:
+            # TODO: Validate that we don't swallow exceptions (unit test?)
+            structlog.stdlib.get_logger("api.error").exception("Uncaught exception")
+            raise
+        finally:
+            process_time = time.perf_counter_ns() - start_time
+            self.access_logger.info(
+                "Request",
+                http={
+                    "url": str(request.url),
+                    "query": dict(request.query_params),
+                    "status_code": response.status_code,
+                    "method": request.method,
+                    "request_id": request_id,
+                    "version": request.scope["http_version"],
+                },
+                client={"ip": request.client.host, "port": request.client.port} if request.client else None,
+                duration=process_time,
+            )
+
+            # TODO: Is this being returned in production? We shouldn't be leaking this.
+            response.headers["X-Process-Time"] = str(process_time / 10 ** 9)
+            
+            return response