Remove State allocs in RedisStateMachine and reduce allocs in ByteArrayCodec

[shikharid]

Two changes:

1. In RedisStateMachine, use pre-allocated State objects
2. For ByteArrayCodec (or any codec that can tell exact encoded byte sizes), directly copy to target ByteBuf instead of creating a temporary single-use copy first

Have added benchmarks (results in comments)

Refer #2610

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[shikharid]

Summary

1. 25% perf improvement in RedisStateMachine with negligible heap allocs (before 130 ns/op, after 104 ns/op)
2. ~10x (1000%) perf improvement in Key/Value encoding for ByteArrayCodec (before 310 ns/op, after 34 ns/op)

Benchmark Setup

• JMH version: 1.21
• VM version: JDK 1.8.0_342, OpenJDK 64-Bit Server VM, 25.342-b07
• OS: MacOS Ventura 13.2.1
• Arch: Apple M1 Max (32 gb, aarch64)
• Warmup: 5 iterations, 10 s each
• Measurement: 5 iterations, 10 s each
• Timeout: 2 s per iteration
• Threads: 1 thread, will synchronize iterations

RedisStateMachine Benchmark Results

Before

Benchmark                                                                  Mode  Cnt    Score    Error   Units
RedisStateMachineBenchmark.measureDecode                                   avgt    5  130.654 ± 11.039   ns/op
RedisStateMachineBenchmark.measureDecode:·gc.alloc.rate                    avgt    5  667.181 ± 55.258  MB/sec
RedisStateMachineBenchmark.measureDecode:·gc.alloc.rate.norm               avgt    5   96.000 ±  0.001    B/op
RedisStateMachineBenchmark.measureDecode:·gc.churn.PS_Eden_Space           avgt    5  667.349 ± 56.391  MB/sec
RedisStateMachineBenchmark.measureDecode:·gc.churn.PS_Eden_Space.norm      avgt    5   96.024 ±  0.745    B/op
RedisStateMachineBenchmark.measureDecode:·gc.churn.PS_Survivor_Space       avgt    5    0.106 ±  0.084  MB/sec
RedisStateMachineBenchmark.measureDecode:·gc.churn.PS_Survivor_Space.norm  avgt    5    0.015 ±  0.011    B/op
RedisStateMachineBenchmark.measureDecode:·gc.count                         avgt    5  715.000           counts
RedisStateMachineBenchmark.measureDecode:·gc.time                          avgt    5  345.000               ms

After

Benchmark                                                     Mode  Cnt    Score    Error   Units
RedisStateMachineBenchmark.measureDecode                      avgt    5  104.293 ±  0.309   ns/op
RedisStateMachineBenchmark.measureDecode:·gc.alloc.rate       avgt    5   ≈ 10⁻⁴           MB/sec
RedisStateMachineBenchmark.measureDecode:·gc.alloc.rate.norm  avgt    5   ≈ 10⁻⁵             B/op
RedisStateMachineBenchmark.measureDecode:·gc.count            avgt    5      ≈ 0           counts

ByteArrayCodec Benchmark Results

Before

ExactVsEstimatedSizeCodecBenchmark.encodeKeyEstimatedSize                                     avgt    5   310.842 ±  1.404   ns/op
ExactVsEstimatedSizeCodecBenchmark.encodeKeyEstimatedSize:·gc.alloc.rate                      avgt    5   972.380 ±  3.934  MB/sec
ExactVsEstimatedSizeCodecBenchmark.encodeKeyEstimatedSize:·gc.alloc.rate.norm                 avgt    5   332.994 ±  0.010    B/op
ExactVsEstimatedSizeCodecBenchmark.encodeKeyEstimatedSize:·gc.churn.PS_Eden_Space             avgt    5   971.755 ± 12.683  MB/sec
ExactVsEstimatedSizeCodecBenchmark.encodeKeyEstimatedSize:·gc.churn.PS_Eden_Space.norm        avgt    5   332.779 ±  3.172    B/op
ExactVsEstimatedSizeCodecBenchmark.encodeKeyEstimatedSize:·gc.churn.PS_Survivor_Space         avgt    5     0.134 ±  0.091  MB/sec
ExactVsEstimatedSizeCodecBenchmark.encodeKeyEstimatedSize:·gc.churn.PS_Survivor_Space.norm    avgt    5     0.046 ±  0.031    B/op
ExactVsEstimatedSizeCodecBenchmark.encodeKeyEstimatedSize:·gc.count                           avgt    5   759.000           counts
ExactVsEstimatedSizeCodecBenchmark.encodeKeyEstimatedSize:·gc.time                            avgt    5   370.000               ms

After

Benchmark                                                                                     Mode  Cnt     Score    Error   Units
ExactVsEstimatedSizeCodecBenchmark.encodeKeyExactSize                                         avgt    5    34.032 ±  0.191   ns/op
ExactVsEstimatedSizeCodecBenchmark.encodeKeyExactSize:·gc.alloc.rate                          avgt    5  4054.084 ± 20.099  MB/sec
ExactVsEstimatedSizeCodecBenchmark.encodeKeyExactSize:·gc.alloc.rate.norm                     avgt    5   152.000 ±  0.001    B/op
ExactVsEstimatedSizeCodecBenchmark.encodeKeyExactSize:·gc.churn.PS_Eden_Space                 avgt    5  4047.560 ± 97.328  MB/sec
ExactVsEstimatedSizeCodecBenchmark.encodeKeyExactSize:·gc.churn.PS_Eden_Space.norm            avgt    5   151.755 ±  3.222    B/op
ExactVsEstimatedSizeCodecBenchmark.encodeKeyExactSize:·gc.churn.PS_Survivor_Space             avgt    5     0.147 ±  0.085  MB/sec
ExactVsEstimatedSizeCodecBenchmark.encodeKeyExactSize:·gc.churn.PS_Survivor_Space.norm        avgt    5     0.006 ±  0.003    B/op
ExactVsEstimatedSizeCodecBenchmark.encodeKeyExactSize:·gc.count                               avgt    5   780.000           counts
ExactVsEstimatedSizeCodecBenchmark.encodeKeyExactSize:·gc.time                                avgt    5   427.000               ms

[mp911de]

Thank you for your contribution. That's merged, polished, and backported now.