[benchmark] Fix copy-paste labels in micro-benchmarks

[thswlsqls]

Purpose

• Correct two non-behavioral copy-paste labels in paimon-micro-benchmarks.
• LookupReaderBenchmark Javadoc described writing; it is a reader benchmark, so the wording now says reading.
• ArrowWriteBenchmark#testWrite created new Benchmark("read", ...), which the harness prints; the benchmark name is now write.

Tests

• Typo/wording fix, no behavior change — no test added. mvn spotless:check -pl paimon-benchmark/paimon-micro-benchmarks passed.
• mvn -pl paimon-benchmark/paimon-micro-benchmarks -DskipTests clean test-compile passed; 17 test sources compiled. Benchmarks were not executed because each @Test runs a long benchmark.