ci: shorten memory benchmark temp root
Use a short mktemp directory under /tmp for the Linux Memory Benchmark before running the existing benchmark command. This avoids the cardano-node Unix socket path limit while keeping other benchmark jobs on runner.temp. Ignore local llm review artifacts and remove the tracked llm review file inherited from the rebased base so the repository keeps llm out of tracked source. Verification: actionlint accepted linux-benchmarks.yml with repository custom runner-label warnings ignored. The representative issue path is 120 bytes, and the new representative socket path is 94 bytes. Live verification: Linux Benchmarks workflow dispatch 25724369765 passed end to end and uploaded memory-bench-results.csv, memory.hp, memory.svg, memory.log, and memory.error.log. Fixes #5283