refactor(tvix/store/pathinfo): test with PathInfoService directly

Since cl/…, a PathInfoService doesn't need to implement `calculate_nar`
anymore, so most of them don't actually have a handle to a
{Blob,Directory}Service anymore.

This means, we can simplify the construction of them for test cases
a lot.

Change-Id: I100e9e1c9b00a049b4d6136c57aad4cdb04461c6
Reviewed-on: https://cl.tvl.fyi/c/depot/+/11691
Reviewed-by: Connor Brewster <cbrewster@hey.com>
Tested-by: BuildkiteCI

tvix/store/src/pathinfoservice/bigtable.rs

@@ -67,6 +67,22 @@ pub struct BigtableParameters {
     app_profile_id: String,
 }
 
+impl BigtableParameters {
+    #[cfg(test)]
+    pub fn default_for_tests() -> Self {
+        Self {
+            project_id: "project-1".into(),
+            instance_name: "instance-1".into(),
+            is_read_only: false,
+            channel_size: default_channel_size(),
+            timeout: default_timeout(),
+            table_name: "table-1".into(),
+            family_name: "cf1".into(),
+            app_profile_id: default_app_profile_id(),
+        }
+    }
+}
+
 fn default_app_profile_id() -> String {
     "default".to_owned()
 }