feat: fix race condition in enforce() causing ArrayIndexOutOfBoundsException

[Copilot]

fix: #511

Race condition in CoreEnforcer.enforce() when policy list is modified during enforcement. Arrays sized with captured policyLen, but loop condition re-reads policy.size(), causing index overflow in concurrent scenarios.

Changes

• CoreEnforcer.java:626: Use captured policyLen in loop condition instead of policy.size()
• ConcurrentEnforcerTest.java: Add regression test exercising concurrent policy modifications during enforcement

// Before
final int policyLen = policy.size();  // Size at time T1
policyEffects = new Effect[policyLen];
matcherResults = new float[policyLen];
for (int i = 0; i < policy.size(); i++) {  // Size at time T2 - may differ
    policyEffects[i] = ...  // ArrayIndexOutOfBoundsException if T2 > T1
}

// After
final int policyLen = policy.size();
policyEffects = new Effect[policyLen];
matcherResults = new float[policyLen];
for (int i = 0; i < policyLen; i++) {  // Consistent with array sizing
    policyEffects[i] = ...
}

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✅ hsluoyz
❌ Copilot
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[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 67.98%. Comparing base (c617f4d) to head (7297e4b).
⚠️ Report is 1 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #513   +/-   ##
=======================================
  Coverage   67.98%   67.98%           
=======================================
  Files          63       63           
  Lines        3089     3089           
  Branches      574      574           
=======================================
  Hits         2100     2100           
  Misses        805      805           
  Partials      184      184           

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