[mod] data: implement a simple currencies (SQL) database (#4836)

To reduce the memory footprint, this patch no longer loads the JSON data
completely into memory.  Instead, there is an SQL database based on
`ExpireCacheSQLite`.

The class CurrenciesDB is a simple DB application that encapsulates the
DB (queries and initialization) and provides convenient methods like
`name_to_iso4217` and `iso4217_to_name`.

Related:

- https://github.com/searxng/searxng/discussions/1892
- https://github.com/searxng/searxng/pull/3458#issuecomment-2900807671
- https://github.com/searxng/searxng/pull/4650

Signed-off-by: Markus Heiser <markus.heiser@darmarit.de>

searxng_extra/update/update_currencies.py

@@ -15,9 +15,7 @@ import json
 
 from searx.locales import LOCALE_NAMES, locales_initialize
 from searx.engines import wikidata, set_loggers
-from searx.data import data_dir
-
-DATA_FILE = data_dir / 'currencies.json'
+from searx.data.currencies import CurrenciesDB
 
 set_loggers(wikidata, 'wikidata')
 locales_initialize()
@@ -149,7 +147,7 @@ def main():
         if len(db['names'][name]) == 1:
             db['names'][name] = db['names'][name][0]
 
-    with DATA_FILE.open('w', encoding='utf8') as f:
+    with CurrenciesDB.json_file.open('w', encoding='utf8') as f:
         json.dump(db, f, indent=4, sort_keys=True, ensure_ascii=False)