[Oracle/Client] Report card database download progress

Card database updates ran invisibly: MTGJSON parsing spun an indeterminate
bar on the UI thread and the set import blocked the window, while the
onboarding wizard spawned `oracle -b` with no progress to show at all.

- Add byte-level scan progress to `RawJson::scanSetRanges` via an optional
  callback, throttled to ~100 reports per scan.
- Emit `OracleImporter::dataReadProgress` during the scan and import sets on a
  worker thread, driving the wizard's progress bar per set.
- With `-b`, write machine-readable `PROGRESS <stage> <done> <total>` lines to
  stdout for the download/scan/import stages; stderr keeps the log output.
- Parse the oracle stdout in `MainWindow` and forward it to the onboarding
  wizard, giving the card database step a determinate bar with stage-specific
  status text.
- Guard the async workers against the wizard being closed mid-run.
- Add Google Test coverage for scan progress reporting.

oracle/src/oraclewizard.h

@@ -52,12 +52,7 @@ public:
     }
     bool saveTokensToFile(const QString &fileName);
 
-    void runInBackground()
-    {
-        backgroundMode = true;
-        hide();
-        currentPage()->initializePage();
-    }
+    void runInBackground();
 
 public:
     OracleImporter *importer;