Improve `RunLengthBitPackingHybridDecoder.readNext` to avoid per-call buffer allocation and `DataInputStream` wrapping

### Describe the enhancement requested

`RunLengthBitPackingHybridDecoder.readNext()` allocates a new `int[]` and `byte[]` on every PACKED-mode call. In workloads that decode many bit-packed runs (definition levels, repetition levels, RLE-encoded integers), these allocations dominate the read-side allocation profile. The upstream code even acknowledges this with a `// TODO: reuse a buffer` comment.

### Problem 1: per-call buffer allocation

[Lines 94–95](https://github.com/apache/parquet-java/blob/4c8f4d4b/parquet-column/src/main/java/org/apache/parquet/column/values/rle/RunLengthBitPackingHybridDecoder.java#L94-L95) allocate fresh arrays on every PACKED-mode `readNext()`:

```java
currentBuffer = new int[currentCount]; // TODO: reuse a buffer
byte[] bytes = new byte[numGroups * bitWidth];
```

`currentCount` is always `numGroups * 8`, and `numGroups` is typically small (1–16 groups = 8–128 values per run). These allocations are individually modest but occur thousands of times per column chunk — once per bit-packed run. In a 180M-row merge with multiple integer/boolean columns, the cumulative allocation is substantial.

Since `currentCount` varies between runs (different `numGroups` values), the fix retains the field-level `int[]` and a new field-level `byte[]`, growing them only when the next run requires a larger buffer.

### Problem 2: per-call DataInputStream wrapping

[Line 98](https://github.com/apache/parquet-java/blob/4c8f4d4b/parquet-column/src/main/java/org/apache/parquet/column/values/rle/RunLengthBitPackingHybridDecoder.java#L98) creates a `new DataInputStream(in)` on every PACKED-mode call:

```java
new DataInputStream(in).readFully(bytes, 0, bytesToRead);
```

This allocates a `DataInputStream` wrapper object per call just to access `readFully()`. A private `readFully()` method on the decoder itself eliminates this allocation and the virtual dispatch through the wrapper.

### Component(s)

Core