Thorns reapply fix (#2338)

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## Pull Request Description
<!-- Describe what this change does and why it is needed -->

Allowed druid cast Thorns on target which already have Thorns on him to
extend duration.
Related with: #2290 

## How to Test the Changes
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1. Invite 2 bot (one of them must be druid which can cast thorns)
2. Select second bot and use commad `cast thorns`
3. Wait until buff timer decrease
4. Use again same command
5. Druid should cast spell

## Impact Assessment
<!-- As a generic test, before and after measure of pmon (playerbot pmon
tick) can help you here. -->
- Does this change increase per-bot/per-tick processing or risk scaling
poorly with thousands of bots?
    - - [x] No, not at all
    - - [ ] Minimal impact (**explain below**)
    - - [ ] Moderate impact (**explain below**)



- Does this change modify default bot behavior?
    - - [x] No
    - - [ ] Yes (**explain why**)



- Does this change add new decision branches or increase maintenance
complexity?
    - - [x] No
    - - [ ] Yes (**explain below**)



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To understand reason.

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## Final Checklist

- - [x] Stability is not compromised.
- - [x] Performance impact is understood, tested, and acceptable.
- - [x] Added logic complexity is justified and explained.
- - [x] Any new bot dialogue lines are translated.
- - [x] Documentation updated if needed (Conf comments, WiKi commands).

## Notes for Reviewers
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src/Ai/Class/Druid/Action/DruidActions.cpp

@@ -11,6 +11,22 @@
 #include "AoeValues.h"
 #include "TargetValue.h"
 
+namespace
+{
+    bool PrepareThornsTarget(PlayerbotAI* botAI, Unit* target)
+    {
+        if (!target)
+            return false;
+
+        Aura* existingThorns = botAI->GetAura("thorns", target, true);
+        if (!existingThorns)
+            return true;
+
+        target->RemoveOwnedAura(existingThorns, AURA_REMOVE_BY_CANCEL);
+        return true;
+    }
+}
+
 std::vector<NextAction> CastAbolishPoisonAction::getAlternatives()
 {
     return NextAction::merge({ NextAction("cure poison") },
@@ -33,6 +49,21 @@ bool CastLifebloomOnMainTankAction::isUseful()
     return !lifebloom || lifebloom->GetStackAmount() < 3 || lifebloom->GetDuration() < 2000;
 }
 
+bool CastThornsAction::Execute(Event event)
+{
+    return PrepareThornsTarget(botAI, GetTarget()) && CastBuffSpellAction::Execute(event);
+}
+
+bool CastThornsOnPartyAction::Execute(Event event)
+{
+    return PrepareThornsTarget(botAI, GetTarget()) && BuffOnPartyAction::Execute(event);
+}
+
+bool CastThornsOnMainTankAction::Execute(Event event)
+{
+    return PrepareThornsTarget(botAI, GetTarget()) && BuffOnMainTankAction::Execute(event);
+}
+
 Value<Unit*>* CastEntanglingRootsCcAction::GetTargetValue()
 {
     return context->GetValue<Unit*>("cc target", "entangling roots");

src/Ai/Class/Druid/Action/DruidActions.h

@@ -114,18 +114,24 @@ class CastThornsAction : public CastBuffSpellAction
 {
 public:
     CastThornsAction(PlayerbotAI* botAI) : CastBuffSpellAction(botAI, "thorns") {}
+
+    bool Execute(Event event) override;
 };
 
 class CastThornsOnPartyAction : public BuffOnPartyAction
 {
 public:
     CastThornsOnPartyAction(PlayerbotAI* botAI) : BuffOnPartyAction(botAI, "thorns") {}
+
+    bool Execute(Event event) override;
 };
 
 class CastThornsOnMainTankAction : public BuffOnMainTankAction
 {
 public:
     CastThornsOnMainTankAction(PlayerbotAI* botAI) : BuffOnMainTankAction(botAI, "thorns", false) {}
+
+    bool Execute(Event event) override;
 };
 
 class CastLifebloomOnMainTankAction : public BuffOnMainTankAction