20: Update PriceAlarmDefinition to support expressions

src/main/tjava/com/r35157/jupiterperpsalarm/impl/ref/PriceAlarmDefinition.tjava

@@ -9,7 +9,7 @@ public record PriceAlarmDefinition(
         int id,
         JupiterPerpsAsset asset,
         PriceDirection direction,
-        BigDecimal target,
+        String targetExpression,
         AlarmTrigger trigger,
         ΩsecondsΩ triggerGracePeriod,
         AlarmSeverity severity,
@@ -18,12 +18,13 @@ public record PriceAlarmDefinition(
     public PriceAlarmDefinition {
         Objects.requireNonNull(asset, "asset");
         Objects.requireNonNull(direction, "direction");
-        Objects.requireNonNull(target, "target");
+        Objects.requireNonNull(targetExpression, "targetExpression");
         Objects.requireNonNull(trigger, "trigger");
+        Objects.requireNonNull(severity, "severity");
         Objects.requireNonNull(note, "note");
 
-        if (target.signum() < 0) {
-            throw new IllegalArgumentException("Target price cannot be negative (was: " + target.signum() + ")!");
+        if (targetExpression.isBlank()) {
+            throw new IllegalArgumentException("Target expression cannot be blank");
         }
 
         if (triggerGracePeriod < 0) {