[fix](nereids)relase physical plan in Profile.releaseMemory() (#57257)

### What problem does this PR solve?
The profile holds a physical plan object. In profile.releaseMemory(),
the physicalPlan needs to be set to null to release it, preventing the
groupExpression in Memo from failing to be released in a timely manner.
Issue Number: close #xxx

Related PR: #xxx

Problem Summary:

### Release note

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- [ ] This is a refactor/code format and no logic has been changed.
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- Behavior changed:
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Author: englefly

fe/fe-core/src/main/java/org/apache/doris/common/profile/Profile.java

@@ -434,6 +434,9 @@ public void setSummaryProfile(SummaryProfile summaryProfile) {
     public void releaseMemory() {
         this.executionProfiles.clear();
         this.changedSessionVarCache = "";
+        this.physicalPlan = null;
+        this.rowsProducedMap = null;
+        this.physicalRelations = null;
     }
 
     public boolean shouldStoreToStorage() {