HBASE-30395 Reduce heap buffer copy in decompression

[Huginn-kio]

HBASE-30395

Summary

Avoid an intermediate heap buffer when reading decompressed stream data into an on-heap ByteBuff.

Root cause

The stream fallback in HFileBlockDefaultDecodingContext uses BlockIOUtils.readFullyWithHeapBuffer, which allocates a temporary heap buffer and copies each read into the destination ByteBuff. This adds an avoidable copy for on-heap destinations.

Fix

• Read directly into the backing array when the destination ByteBuff exposes one.
• Preserve the existing temporary-buffer fallback for direct or non-array ByteBuff instances.
• Use the new helper for compressed stream fallback and uncompressed stream reads.
• Add regression coverage for both the direct-read and fallback paths.

Compatibility

• Public API impact: none; BlockIOUtils remains internal.
• Configuration impact: none.
• Persisted file format impact: none.
• Wire format impact: none.

Testing

• mvn -pl hbase-server -am -Dtest=TestBlockIOUtils -DfailIfNoTests=false -DskipITs test
• mvn -pl hbase-common -DskipTests -Dcheckstyle.includes="**/BlockIOUtils.java,**/HFileBlockDefaultDecodingContext.java" checkstyle:check
• mvn -pl hbase-server -DskipTests -Dcheckstyle.includes="**/TestBlockIOUtils.java" checkstyle:check