Fix Direct IO and drop cache silent failures on Ubuntu Linux

[Copilot]

Direct IO with the modern engine silently failed in jpackage DEB/RPM builds, and the sync command could be abandoned prematurely before drop_caches ran — both producing no visible error output.

Root causes & fixes

• jdk.unsupported missing from jpackage module list (build.xml)
  com.sun.nio.file.ExtendedOpenOption (used for O_DIRECT) is exported from jdk.unsupported, which was absent from --add-modules in both create-fat-deb and create-fat-rpm targets. The bundled JRE threw NoClassDefFoundError at runtime — silently, because BenchmarkWorker.done() never called get().

  <!-- before -->
  java.base,java.desktop,java.logging,...,java.naming
  <!-- after -->
  java.base,java.desktop,java.logging,...,java.naming,jdk.unsupported

• InterruptedException swallowed in sync/drop_caches commands (UtilOs.java)
  A lingering interrupt on the SwingWorker thread (e.g. from a prior cancellation) caused process.waitFor() to throw immediately, abandoning sync before it completed. flushDataToDriveLinux() and dropWriteCacheLinux() now retry waitFor() in a loop on interruption and restore the interrupted status afterward.

• Null FileChannel on Direct IO IOException fallback (Sample.java)
  If FileChannel.open() with ExtendedOpenOption.DIRECT threw IOException (e.g. filesystem doesn't support O_DIRECT), initialFc was left null and the subsequent fc.read()/fc.write() call threw NullPointerException — not caught by the IOException handler. Both measureWrite() and measureRead() now fall back to buffered IO with an explicit error message, matching the existing UnsupportedOperationException path.

• Silent exception swallowing in BenchmarkWorker (BenchmarkWorker.java)
  done() never called get(), so any exception from doInBackground() was silently discarded. Now logs and surfaces the error message to the user.

Original prompt

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This section details on the original issue you should resolve

<issue_title>ubuntu: direct io / drop cache sudo command does not work</issue_title>
<issue_description>testing with @mikewong79 discovered that

running as root should run drop cache and clear the disk cache but this did not work:

it is suspected the drop cache also does not work

</issue_description>

<agent_instructions>help investigate and resolve why direct io w modern engine does not work on ubuntu linux. there is no output when it fails.</agent_instructions>

Comments on the Issue (you are @copilot in this section)

@jamesmarkchan mike testing on a usb drive live image:

mikes usb hw:

https://www.amazon.com/dp/B01BGTG2A0?ref=ppx_pop_mob_ap_share</comment_new>
<comment_new>@jamesmarkchan
running directIO in NetBeans IDS appears to work in ubuntu... it's just the jpackage deb installer that does not work.

</comment_new>

• Fixes ubuntu: direct io / drop cache sudo command does not work #144

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