TestDefaultCodecParallelizesIO.testTermsSeekExact fails

### Description

On 10x, this seed fails repeatably with trace:

```
TestDefaultCodecParallelizesIO > testTermsSeekExact FAILED
java.lang.AssertionError
at __randomizedtesting.SeedInfo.seed([188E78701153935C:1CA56CB7693DFC05]:0)
at org.junit.Assert.fail(Assert.java:87)
at org.junit.Assert.assertTrue(Assert.java:42)
at org.junit.Assert.assertTrue(Assert.java:53)
at org.apache.lucene.index.TestDefaultCodecParallelizesIO.testTermsSeekExact(TestDefaultCodecParallelizesIO.java:89)
at java.base/jdk.internal.reflect.DirectMethodHandleAccessor.invoke(DirectMethodHandleAccessor.java:103)
at java.base/java.lang.reflect.Method.invoke(Method.java:580)
at com.carrotsearch.randomizedtesting.RandomizedRunner.invoke(RandomizedRunner.java:1758)
at com.carrotsearch.randomizedtesting.RandomizedRunner$8.evaluate(RandomizedRunner.java:946)
at com.carrotsearch.randomizedtesting.RandomizedRunner$9.evaluate(RandomizedRunner.java:982)
at com.carrotsearch.randomizedtesting.RandomizedRunner$10.evaluate(RandomizedRunner.java:996)
at org.apache.lucene.tests.util.TestRuleSetupTeardownChained$1.evaluate(TestRuleSetupTeardownChained.java:48)
at org.apache.lucene.tests.util.AbstractBeforeAfterRule$1.evaluate(AbstractBeforeAfterRule.java:43)
at org.apache.lucene.tests.util.TestRuleThreadAndTestName$1.evaluate(TestRuleThreadAndTestName.java:45)
at org.apache.lucene.tests.util.TestRuleIgnoreAfterMaxFailures$1.evaluate(TestRuleIgnoreAfterMaxFailures.java:60)
at org.apache.lucene.tests.util.TestRuleMarkFailure$1.evaluate(TestRuleMarkFailure.java:44)
```

I am going to run with many iterations on main to see if another seed reproduces there.

### Gradle command to reproduce

```
./gradlew :lucene:core:test --tests "org.apache.lucene.index.TestDefaultCodecParallelizesIO.testTermsSeekExact" -Ptests.jvms=5 "-Ptests.jvmargs=-XX:TieredStopAtLevel=1 -XX:+UseParallelGC -XX:ActiveProcessorCount=1" -Ptests.seed=188E78701153935C -Ptests.locale=en-KN -Ptests.timezone=Asia/Hebron -Ptests.gui=false -Ptests.file.encoding=UTF-8 -Ptests.vectorsize=512 -Ptests.forceintegervectors=true
```

Start by running the provided Gradle command and inspect org.apache.lucene.index.TestDefaultCodecParallelizesIO.testTermsSeekExact at line 89, including the surrounding test setup. Trace the failure through the default codec's terms-seeking and parallelized I/O behavior. Done means the test passes reliably across repeated runs without weakening its assertions.

Written by the indexing model from the issue text.