port client CPU optimizations to hbase_2.0

[hhlgt]

Summary

This PR ports the request/response hot-path optimizations from
obkv-table-client-java to the HBase 2.x client.

It reduces CPU usage and temporary object allocation in HBase Get, Batch Get,
Scan, and Put operations while preserving the existing HBase client APIs and
legacy decoding paths.

Changes

Read path

• Consume compact ObHBaseCellBatch results directly for:
  • point Get
  • Batch Get
  • Scan
  • Query-and-Mutate results
• Introduce OHBaseResultCell, an immutable Cell implementation backed
  directly by decoded K/Q/T/V arrays.
• Avoid materializing intermediate List<ObObj> and unnecessary KeyValue
  copies on the compact result path.
• Optimize pure-Get batch result mapping and preallocate result containers.
• Reuse row-key arrays when assembling point Get and closestRowBefore results.
• Preserve HBase cell ordering by family, qualifier, and descending timestamp.
• Keep the generic ObObj/KeyValue path as a compatibility fallback.

Write path

• Build HBase Put V2 requests using the compact cell representation provided by
  obkv-table-client-java.
• Preallocate key, column-family, and cell containers.
• Reuse contiguous qualifier/value byte arrays during synchronous request
  encoding.
• Use ObBytesString views for sliced cell regions to avoid unnecessary clones.
• Avoid duplicate value cloning when encoding Put cells with TTL.
• Validate Put mutations directly from the original family/cell map without
  materializing deprecated compatibility structures.

Compatibility and safety

• Preserve existing Table, Result, and Cell behavior.
• Support both single-column-family and TableGroup result formats.
• Preserve empty-result and existence-only Get semantics.
• Validate malformed K/Q/T/V results and unexpected point-Get row keys.
• Keep legacy result decoding available when compact results are unavailable.

Dependency

• Upgrade obkv-table-client from 2.4.0 to 2.4.1-SNAPSHOT.
• This PR depends on the corresponding CPU optimization changes in
  obkv-table-client-java.

Dependent PR: oceanbase/obkv-table-client-java#442

Tests

Added focused unit tests covering:

• compact Batch Get result conversion and request ordering
• compact Put request construction with and without TTL
• point Get and closestRowBefore result processing
• compact Scan result consumption
• zero-copy/sliced qualifier and value handling
• Put validation and maximum cell-size boundaries
• OHBaseResultCell compatibility and TableGroup field ranges
• malformed and empty result handling

Focused test result: 39 tests passed with 0 failures and 0 errors.

[hhlgt]

AI Coding Review

审查范围：
Base: origin/hbase_2.0
Head: optimize/client-cpu-performance-hbase_2.0
Commits: 1
Target: HBase 2.x

[P1] BufferedMutatorParams.maxKeyValueSize 被静默忽略

位置：[OHBufferedMutatorImpl.java (line 184)]
HBase 2.x 版本存在与 master PR 相同的问题：
private final int maxKeyValueSize;
该字段从 BufferedMutatorParams 正确初始化，但 Put 校验改为：
ohTable.validatePutMutation((Put) mt);
导致字段后续完全未被使用，实际校验采用 OHTable 自身配置。
影响和修复方式与 master PR 相同：需要向 validatePutMutation 传入当前 mutator 的 maxKeyValueSize，并增加参数覆盖优先级测试。

依赖风险

同样依赖：
<table.client.version>2.4.1-SNAPSHOT</table.client.version>
需要确保 Table Client PR 先合入并发布可解析的 snapshot 或正式版本。

Review 结论

合入前需要修复 Mutator 参数失效问题，并验证依赖发布。

[WeiXinChan]

LGTM