ORC-624: [C++] Avoid unaligned trailer loads in LZO decompressor

[wgtmac]

What changes were proposed in this pull request?

This PR replaces two potentially unaligned 16-bit trailer loads with an alignment-safe little-endian reader.

It also adds a long-distance match test covering the previously untested 0x10 LZO command path. This is a focused replacement for the LZO portion of #496, which was closed without merging.

Why are the changes needed?

The LZO input pointer advances byte by byte and is not guaranteed to be 2-byte aligned. Dereferencing it as uint16_t* or int16_t* is undefined behavior and is reported by UBSan.

How was this patch tested?

cmake --build build --target orc-test -j8
cd build/c++/test
./orc-test --gtest_filter='TestDecompression.testLzoLong:TestDecompression.testLzoLongDistanceMatch:TestDecompression.testLzoOverflow:TestDecompression.testLzoTruncatedStopCommand'

All four tests passed. The existing long test covers the 0x20 command path, and the new test covers the 0x10 path.

Was this patch authored or co-authored using generative AI tooling?

Generated-by: OpenAI Codex (GPT-5)

[ffacs]

LGTM