during bluetooth_ble matching, convert major and minor to hexadecimal

The background/bluetooth_ble data type has "major" and "minor" as decimal integers. (e-mission/e-mission-docs#1062 (comment))
But in the vehicle_identities spec, we have major:minor pairs as hexadecimal strings. So we will need to convert.

decimalToHex handles this and allows us to add padding, ensuring the converted major and minor are always 4 hex characters.
(so 1 becomes "0001", 255 becomes "00ff", etc.)

www/js/survey/inputMatcher.ts

@@ -379,6 +379,19 @@ function getBleScansForTimelineEntry(
   return bleScans.filter((scan) => validBleScanForTimelineEntry(tlEntry, scan));
 }
 
+/**
+ * @description Convert a decimal number to a hexadecimal string, with optional padding
+ * @example decimalToHex(245) => 'f5'
+ * @example decimalToHex(245, 4) => '00f5'
+ */
+function decimalToHex(d: string | number, padding?: number) {
+  let hex = Number(d).toString(16);
+  while (hex.length < (padding || 0)) {
+    hex = '0' + hex;
+  }
+  return hex;
+}
+
 export function mapBleScansToTimelineEntries(allEntries: TimelineEntry[], appConfig: AppConfig) {
   const timelineBleMap = {};
   for (const tlEntry of allEntries) {
@@ -390,7 +403,9 @@ export function mapBleScansToTimelineEntries(allEntries: TimelineEntry[], appCon
     // count the number of occurrences of each major:minor pair
     const majorMinorCounts = {};
     matches.forEach((match) => {
-      const majorMinor = match.data.major + ':' + match.data.minor;
+      const major = decimalToHex(match.data.major, 4);
+      const minor = decimalToHex(match.data.minor, 4);
+      const majorMinor = major + ':' + minor;
       majorMinorCounts[majorMinor] = majorMinorCounts[majorMinor]
         ? majorMinorCounts[majorMinor] + 1
         : 1;