[Oracle] Parse sets lazily to slash importer peak memory

- Add a raw JSON scanner that splits the document into per-set byte ranges
  without materializing the JSON tree
- Keep only the raw document bytes and parse one set at a time in startImport
- Take readSetsFromByteArray by value so the wizard's buffer is moved, not copied
- Clear the retained raw data in releaseSetData()/clear()
- Cover the scanner and lazy parsing with tests

Took 2 minutes

oracle/CMakeLists.txt

@@ -23,6 +23,7 @@ set(oracle_SOURCES
     src/pages.cpp
     src/pagetemplates.cpp
     src/parsehelpers.cpp
+    src/raw_json_scanner.cpp
     ../cockatrice/src/client/settings/cache_settings.cpp
     ../cockatrice/src/client/settings/card_counter_settings.cpp
     ../cockatrice/src/client/settings/shortcuts_settings.cpp