Surface ipinfo.io location check failures

Closes #1311.

The ipinfo.io lookup in AnophelesBase swallowed every OSError silently,
leaving _client_details = None. That cascaded into _get_gcp_region()
returning None and the GCS URL optimisation falling back to the default
bucket without any indication that the location check had failed.

Researchers on restricted networks (corporate firewalls, institutional
VPNs, regions where ipinfo.io is blocked) hit this path the most, and
had no way to correlate slow downloads with a failed lookup.

Now the failure is logged at DEBUG level for users running with
debug=True, and a UserWarning is emitted explaining the fallback and
pointing to the `url` parameter as a manual override. The fallback
behaviour itself is unchanged.

Author: kunal-10-cloud

malariagen_data/anoph/base.py

@@ -103,8 +103,16 @@ def __init__(
         if check_location:
             try:
                 self._client_details = ipinfo.getHandler().getDetails()
-            except OSError:
-                pass
+            except OSError as exc:
+                self._log.debug(f"Location check failed: {exc}")
+                warnings.warn(
+                    "Could not determine client location via ipinfo.io "
+                    f"({exc}). Region-optimal GCS bucket selection is "
+                    "unavailable. You can manually specify a region using "
+                    "the `url` parameter.",
+                    UserWarning,
+                    stacklevel=2,
+                )
 
         # Determine cloud location details.
         self._gcp_region = _get_gcp_region(self._client_details)