test(qwp): record JDK-8 verification of the recovery mmap-fault mechanism (#64 M2)

The recovery fix rests on HotSpot delivering a catchable InternalError
(message containing "unsafe memory access operation") at an Unsafe access and
on a direct try/catch catching it. Prior review verified this on JDK 17/21/25
and inferred JDK 8 from the adjacent pre-21 LTS releases, but JDK 8 is the
shipping/CI source of truth and the original flake was on a JDK-8 ZFS runner,
so it had to be checked there directly.

Verified on Temurin 1.8.0_492: MmapSegmentRecoveryFaultTest passes 5/5 in both
-Xint and JIT modes; HotSpot emits "a fault occurred in a recent unsafe memory
access operation in compiled Java code"; a direct try/catch catches the fault
in interpreter, C1, and C2 modes; isMmapAccessFault's shared fragment matches
while the JDK 21+-only needle it replaced does not. The build-jdk8 CI job
already runs this test on JDK 8 on every push, so the gate stays enforced.
Documents the result in the test's class javadoc; no behavior change.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

Author: puzpuzpuz

core/src/test/java/io/questdb/client/test/cutlass/qwp/client/sf/cursor/MmapSegmentRecoveryFaultTest.java

@@ -63,6 +63,14 @@
  *       so a reflection-based test spuriously fails on the shipping JDK 8/11/17
  *       even though the direct-call production path catches it fine.</li>
  * </ul>
+ * The fault-delivery mechanism the fix rests on was verified directly on the
+ * shipping/CI Java floor -- JDK 8 (Temurin 1.8.0_492) -- not merely inferred
+ * from the adjacent pre-21 LTS releases: the whole class passes there in both
+ * interpreter ({@code -Xint}) and JIT modes, HotSpot emits the exact pre-21
+ * message above, and a <i>direct</i> {@code try/catch} catches the fault in
+ * interpreter, C1, and C2 modes. {@code isMmapAccessFault}'s shared
+ * {@code "unsafe memory access operation"} fragment matches that message while
+ * the JDK 21+-only needle it replaced does not -- the guard is live on JDK 8.
  * The unbacked tail is produced portably by truncating the file down (dropping
  * the tail blocks) and back up to the mapping size (leaving a sparse hole). A
  * hole-faulting filesystem (ZFS) then faults on the read exactly as in