Truly unchecked getters

### Describe the enhancement requested

Right now the library integrating with arrow-java needs to resort to hacks of setting environment variable or system property at runtime if it knows its usages of arrow-java can omit null and bounds checking. However, that is not true for all of the usages in the given process leading to invalid data reads or segfaults.

To avoid this pitfall I suggest we add getUnchecked apis that NEVER do any null and bound checking but put the responsibility on the caller to guard against their possibility. For example in apache iceberg https://github.com/apache/iceberg/blob/23b5ce8eeca2d894c7973e19caa5c5ec02b4e4b8/spark/v4.1/spark/src/main/java/org/apache/iceberg/spark/data/vectorized/VectorizedSparkParquetReaders.java#L44-L51

These apis would make it easy to mix libraries that use arrow as an implementation detail along with user code that operates directly on arrow arrays

首先检查现有的 Arrow 数组 getter API，以及链接行中 Iceberg 的 VectorizedSparkParquetReaders.java 对未经检查访问的使用情况。Issue 未指出任何 arrow-java 文件或测试，因此请先确定受影响的 getter 系列和测试位置。完成标准是所请求的未经检查 API 均可一致地使用，并且测试覆盖由调用方负责的行为。

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