fix: address Copilot review feedback on benchmark code

Remove unused ExpandoMetaClass import from CallSiteInvalidationBench.

Clarify Javadoc on dynamicFinderCalls and mixedCompiledAndDynamicFinders
to state that injection cost is intentionally included since these model
per-request GORM behavior.

Replace System.nanoTime() with a deterministic counter for metaclass
property name variation in fullAnalysisWithInvalidation to eliminate
unrelated overhead and improve run-to-run comparability.

Author: jamesfredley

subprojects/performance/src/jmh/groovy/org/apache/groovy/perf/grails/CallSiteInvalidationBench.groovy

@@ -18,7 +18,6 @@
  */
 package org.apache.groovy.perf.grails
 
-import groovy.lang.ExpandoMetaClass
 import groovy.lang.GroovySystem
 
 import org.openjdk.jmh.annotations.*

subprojects/performance/src/jmh/groovy/org/apache/groovy/perf/grails/GrailsWorkloadBench.groovy

@@ -103,6 +103,7 @@ class GrailsWorkloadBench {
     List<Employee> employees
     List<Project> projects
     List<Task> tasks
+    int invalidationCounter
 
     @Setup(Level.Iteration)
     void setup() {
@@ -430,7 +431,7 @@ class GrailsWorkloadBench {
     @Benchmark
     void fullAnalysisWithInvalidation(Blackhole bh) {
         // Ongoing framework metaclass activity
-        PluginConfig.metaClass."preRequest${System.nanoTime() % 3}" = { -> 'init' }
+        PluginConfig.metaClass."preRequest${invalidationCounter++ % 3}" = { -> 'init' }
 
         // Employee analysis
         def activeEmps = employees.findAll { it.isActive }
@@ -444,7 +445,7 @@ class GrailsWorkloadBench {
         }
 
         // Mid-request metaclass change
-        PluginConfig.metaClass."midRequest${System.nanoTime() % 3}" = { -> 'lazy' }
+        PluginConfig.metaClass."midRequest${invalidationCounter++ % 3}" = { -> 'lazy' }
 
         // Project metrics
         def projectSummary = projects.collect { proj ->

subprojects/performance/src/jmh/groovy/org/apache/groovy/perf/grails/MetaclassVariationBench.groovy

@@ -203,7 +203,7 @@ class MetaclassVariationBench {
         bh.consume(sum)
     }
 
-    /** Calling dynamic finders injected via static metaclass. */
+    /** Injection + invocation of dynamic finders via static metaclass (models per-request GORM cost). */
     @Benchmark
     void dynamicFinderCalls(Blackhole bh) {
         // Inject dynamic finders
@@ -222,7 +222,7 @@ class MetaclassVariationBench {
         }
     }
 
-    /** Mixed compiled method calls and dynamic finder calls. */
+    /** Mixed compiled method calls and dynamic finder injection + invocation (models per-request GORM cost). */
     @Benchmark
     void mixedCompiledAndDynamicFinders(Blackhole bh) {
         DomainEntity.metaClass.static.findByName = { String n ->