Bump to 0.1.1: fix bugs, rewrite tests

Bug fixes:
- Fix Zeller's formula for Julian calendar (separate branch without
  century correction) and use rem_euclid for negative modulo safety
- Pass country code (cc=) to isdayoff.ru API in holiday plugin
- Sync clap --version with Cargo.toml (was hardcoded "1.0.0")

Tests:
- Rename integration_tests.rs to unit_tests.rs (they are unit tests)
- Fix race condition on env vars in plugin tests (Mutex + remove_var)
- Fix incorrect assertions (color tty detection, locale fallback)
- Add missing test cases: Julian/Gregorian Zeller, display date
  parsing, Sunday offset, week numbers, edge cases (87 tests total)
- Remove brittle version-checking tests

plugins/holiday_highlighter/tests/integration_tests.rs

@@ -1,56 +0,0 @@
-//! Integration tests for holiday_highlighter plugin.
-
-use holiday_highlighter::{
-    PLUGIN_NAME, PLUGIN_VERSION, get_country_from_locale, plugin_get_name, plugin_get_version,
-};
-use std::ffi::CStr;
-
-#[test]
-fn test_get_country_from_locale_ru() {
-    unsafe {
-        std::env::set_var("LC_ALL", "ru_RU.UTF-8");
-    }
-    assert_eq!(get_country_from_locale(), "RU");
-}
-
-#[test]
-fn test_get_country_from_locale_us() {
-    unsafe {
-        std::env::set_var("LC_ALL", "en_US.UTF-8");
-    }
-    assert_eq!(get_country_from_locale(), "US");
-}
-
-#[test]
-fn test_get_country_from_locale_by() {
-    unsafe {
-        std::env::set_var("LC_ALL", "be_BY.UTF-8");
-    }
-    assert_eq!(get_country_from_locale(), "BY");
-}
-
-#[test]
-fn test_get_country_from_locale_fallback() {
-    unsafe {
-        std::env::set_var("LC_ALL", "");
-        std::env::set_var("LC_TIME", "");
-        std::env::set_var("LANG", "");
-    }
-    assert_eq!(get_country_from_locale(), "RU");
-}
-
-#[test]
-fn test_plugin_metadata_from_cargo() {
-    assert_eq!(PLUGIN_NAME, "holiday_highlighter");
-    assert_eq!(PLUGIN_VERSION, "0.1.0");
-}
-
-#[test]
-fn test_plugin_get_name_version() {
-    unsafe {
-        let name = CStr::from_ptr(plugin_get_name()).to_str().unwrap();
-        let version = CStr::from_ptr(plugin_get_version()).to_str().unwrap();
-        assert_eq!(name, "holiday_highlighter");
-        assert_eq!(version, "0.1.0");
-    }
-}

plugins/holiday_highlighter/tests/unit_tests.rs

@@ -0,0 +1,80 @@
+//! Unit tests for holiday_highlighter plugin.
+
+use std::sync::Mutex;
+
+use holiday_highlighter::get_country_from_locale;
+
+/// Mutex to serialize tests that modify environment variables.
+/// `set_var` is not thread-safe, so locale tests must not run in parallel.
+/// We use `lock().unwrap_or_else(|e| e.into_inner())` to recover from poison.
+static ENV_LOCK: Mutex<()> = Mutex::new(());
+
+fn lock_env() -> std::sync::MutexGuard<'static, ()> {
+    ENV_LOCK.lock().unwrap_or_else(|e| e.into_inner())
+}
+
+/// Reset all locale env vars to a clean state, then set `LC_ALL` to the given value.
+fn set_locale(lc_all: &str) {
+    unsafe {
+        std::env::set_var("LC_ALL", lc_all);
+        std::env::remove_var("LC_TIME");
+        std::env::remove_var("LANG");
+    }
+}
+
+/// Remove all locale env vars.
+fn clear_locale() {
+    unsafe {
+        std::env::remove_var("LC_ALL");
+        std::env::remove_var("LC_TIME");
+        std::env::remove_var("LANG");
+    }
+}
+
+// ---------------------------------------------------------------------------
+// Country detection from locale
+// ---------------------------------------------------------------------------
+
+#[test]
+fn country_from_locale_ru() {
+    let _guard = lock_env();
+    set_locale("ru_RU.UTF-8");
+    assert_eq!(get_country_from_locale(), "RU");
+}
+
+#[test]
+fn country_from_locale_us() {
+    let _guard = lock_env();
+    set_locale("en_US.UTF-8");
+    assert_eq!(get_country_from_locale(), "US");
+}
+
+#[test]
+fn country_from_locale_by() {
+    let _guard = lock_env();
+    set_locale("be_BY.UTF-8");
+    assert_eq!(get_country_from_locale(), "BY");
+}
+
+#[test]
+fn country_from_locale_kz() {
+    let _guard = lock_env();
+    set_locale("kk_KZ.UTF-8");
+    assert_eq!(get_country_from_locale(), "KZ");
+}
+
+#[test]
+fn country_from_locale_fallback_to_us() {
+    let _guard = lock_env();
+    clear_locale();
+    // When no locale vars are set, the function defaults to "en_US.UTF-8" -> "US"
+    assert_eq!(get_country_from_locale(), "US");
+}
+
+#[test]
+fn country_from_locale_lc_time_fallback() {
+    let _guard = lock_env();
+    clear_locale();
+    unsafe { std::env::set_var("LC_TIME", "tr_TR.UTF-8") };
+    assert_eq!(get_country_from_locale(), "TR");
+}