✅ **Add tests for LangCountry data resolution and Latvian overrides**

- ➕ Introduced `LangCountryDataAvailabilityTest` to validate data file availability and integrity for allowed `lang-country` codes.
- 🛠️ Added Latvian (`lv-LV`) override JSON file with localized settings and validation.
- 🧪 Verified graceful switching between `lang-country` sessions in tests.

lang/lang-country-overrides/lv-LV.json

@@ -0,0 +1,19 @@
+{
+  "country": "LV",
+  "country_name": "Latvia",
+  "country_name_local": "Latvija",
+  "lang": "lv",
+  "name": "Latviešu",
+  "date_numbers": "d.m.Y",
+  "date_numbers_full_capitals": "DD.MM.YYYY",
+  "date_words_without_day": "Y. \\g\\a\\d\\a j. F",
+  "date_words_with_day": "l, Y. \\g\\a\\d\\a j. F",
+  "date_birthday": "j. F",
+  "time_format": "H:i",
+  "emoji_flag": "🇱🇻",
+  "currency_code": "EUR",
+  "currency_symbol": "€",
+  "currency_symbol_local": "€",
+  "currency_name": "Euro",
+  "currency_name_local": "eiro"
+}