Benchmarks: make jmh.gradle run cleanly on JDK 17 (module opens, configurable heap, failOnError)

### Problem
The JMH harness fails on a clean JDK 17 checkout:
1. Spark 4.x reflects into `sun.util.calendar`; without `--add-opens` the read-path benchmarks throw
`IllegalAccessException` at warm-up (stack trace below).
2. Heap is hard-coded to `-Xmx32g`; the full-scale `PlanningBenchmark` `...WithStats` OOMs at that size.
3. `failOnError = true` aborts the whole suite (and discards completed results) on one failure.

### Reproduce (JDK 17, Corretto 17.0.19)
```
./gradlew -PsparkVersions=3.5 -PscalaVersion=2.12 \
:iceberg-spark:iceberg-spark-extensions-3.5_2.12:jmh \
-PjmhIncludeRegex=IcebergSourceParquetEqDeleteBenchmark \
-PjmhOutputPath=build/reports/jmh/human.txt \
-PjmhJsonOutputPath=build/reports/jmh/results.json
```
=> `IllegalAccessException: sun.util.calendar.ZoneInfo`

Example failure (from earlier EC2 run):
```
org.apache.spark.SparkException: Job aborted due to stage failure:
Task 0 in stage 0.0 failed 1 times ...
java.lang.IllegalAccessException: symbolic reference class is not accessible:
class sun.util.calendar.ZoneInfo, from interface
org.apache.spark.sql.catalyst.util.SparkDateTimeUtils (unnamed module)
at java.base/java.lang.invoke.MemberName.makeAccessException(MemberName.java:955)
at org.apache.spark.sql.catalyst.util.SparkDateTimeUtils.toJavaDate(SparkDateTimeUtils.scala:304)
at org.apache.iceberg.spark.source.IcebergSourceBenchmark.appendAsFile(IcebergSourceBenchmark.java:136)
```

### Proposal
Add the JDK 17 `--add-opens` set to JMH `jvmArgs`, make heap configurable via `-PjmhHeap` (default `32g`),
and make `failOnError` configurable via `-PjmhFailOnError` (default `true`). One file: `jmh.gradle`.

### Evidence
- Failure: read-path benchmarks crash at warm-up without `sun.util.calendar` open
- Success: same suites complete on Corretto 17.0.19 / JMH 1.37 on EC2 `r7i.4xlarge` / `r7i.8xlarge` when the opens set and a larger heap (`-PjmhHeap=220g` for full-scale planning) are applied
- Defaults preserved: heap stays `32g` and `failOnError` stays `true` unless `-P` flags are passed

Sharing PR with fix

Start with the one named file, jmh.gradle, and run the provided Gradle JMH command on JDK 17 to reproduce the ZoneInfo IllegalAccessException. Verify that the JDK 17 module opens are applied, -PjmhHeap and -PjmhFailOnError override their documented defaults, and benchmark results remain available when a failure occurs.

Written by the indexing model from the issue text.