Fix European trip return heuristic for weekend location tracking

Adjust European short trip heuristic from >3 days to >1 day to correctly
detect when user has returned home from European trips. This fixes the
April 29-30, 2023 case where the location incorrectly showed "Sankt Georg, Hamburg"
instead of "Bristol" when the user was free (no events scheduled) after
the foss-north trip ended on April 27.

The previous logic required more than 3 days to pass before assuming
return home from European countries, but for short European trips by
rail/ferry, users typically return within 1-2 days.

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

node_modules/eslint/lib/rules/utils/regular-expressions.js

@@ -0,0 +1,42 @@
+/**
+ * @fileoverview Common utils for regular expressions.
+ * @author Josh Goldberg
+ * @author Toru Nagashima
+ */
+
+"use strict";
+
+const { RegExpValidator } = require("@eslint-community/regexpp");
+
+const REGEXPP_LATEST_ECMA_VERSION = 2024;
+
+/**
+ * Checks if the given regular expression pattern would be valid with the `u` flag.
+ * @param {number} ecmaVersion ECMAScript version to parse in.
+ * @param {string} pattern The regular expression pattern to verify.
+ * @returns {boolean} `true` if the pattern would be valid with the `u` flag.
+ * `false` if the pattern would be invalid with the `u` flag or the configured
+ * ecmaVersion doesn't support the `u` flag.
+ */
+function isValidWithUnicodeFlag(ecmaVersion, pattern) {
+    if (ecmaVersion <= 5) { // ecmaVersion <= 5 doesn't support the 'u' flag
+        return false;
+    }
+
+    const validator = new RegExpValidator({
+        ecmaVersion: Math.min(ecmaVersion, REGEXPP_LATEST_ECMA_VERSION)
+    });
+
+    try {
+        validator.validatePattern(pattern, void 0, void 0, { unicode: /* uFlag = */ true });
+    } catch {
+        return false;
+    }
+
+    return true;
+}
+
+module.exports = {
+    isValidWithUnicodeFlag,
+    REGEXPP_LATEST_ECMA_VERSION
+};