Performance-related microcleanup

[mdindoffer]

Perform small cleanups and optimizations that positively impact performance.

• Remove unnecessary bitwise and in WirePointer
• Remove always true condition in Serialize
• Pre-size segment ArrayList in Serialize
• Remove unused local var in Serialize
• Remove unnecessary bit shift in PackedOutputStream#write
• Make fields final in BuilderArena and Serialize
• Make Iterator classes static in DataList and TextList
• Pre-size ArrayList in ReaderArena constructor

[dwrensha]

Thanks! How much of a speedup are you seeing with these changes?

[mdindoffer]

Nothing huge, these are really minor changes.

In synthetic benchmarks of deserialization I gain consistently about 7% - 10% improvement in throughput on JDK17. https://gist.github.com/mdindoffer/dd0bb4661a181127939e75846c4fe3a4

Before

Benchmark                            Mode  Cnt         Score        Error  Units
MyBenchmark.benchmarkSerializeRead  thrpt   50  15686722.743 ± 973023.487  ops/s

After

Benchmark                            Mode  Cnt         Score        Error  Units
MyBenchmark.benchmarkSerializeRead  thrpt   50  17242835.294 ± 148983.346  ops/s