Fix #1998: use try-with-resources in test file utilities

[elharo]

Fixes #1998

Convert manual try-catch-finally stream handling to try-with-resources in the test utilities:

• TestFileUtils: copyFile, readBytes, writeBytes, readProps, writeProps
• TestFileProcessor: write(File, String), write(File, InputStream), copy(File, File, ProgressListener)

Resources created inside each method are now closed reliably (with close exceptions properly suppressed), eliminating the leak when an explicit close() throws before the finally block. The caller-supplied InputStream in TestFileProcessor.write/copy remains intentionally unclosed, matching prior behavior.

No new tests required.

[gnodet]

LGTM — Clean, correct conversion of 8 methods across two test utility files from manual try-catch-finally to try-with-resources. All conversions are behavior-preserving:

• The mkdirs reordering in copy/copyFile is safe and actually a slight improvement (no resources open when mkdirs runs).
• The caller-supplied InputStream in TestFileProcessor.write(File, InputStream) remains correctly unmanaged.
• Exception suppression via try-with-resources is strictly better for diagnostics than the original swallowed close exceptions.
• Net -130 lines of boilerplate with no functional risk.

CI should pass before merge.

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Claude Code on behalf of gnodet