DeltaByteArrayDecoder panics on invalid prefix lengths

[pchintar]

Problem

DeltaByteArrayDecoder::get assumes decoded prefix lengths are always valid and directly slices:

self.previous_value[0..prefix_len]

If the decoded prefix_len is negative (after decoding) or larger than
previous_value.len(), this results in a slice bounds panic.

Expected Behavior

The decoder should return Err on invalid input instead of panicking.

Actual Behavior

Invalid prefix lengths can cause a panic such as:

range end index X out of range for slice of length Y

Reproduction

This can be reproduced by:

• encoding valid DELTA_BYTE_ARRAY data
• modifying the prefix-length stream (DELTA_BINARY_PACKED)
• decoding using DeltaByteArrayDecoder::get

This leads to a panic instead of returning an error.

Notes

• There is currently no validation for:
  • negative prefix lengths
  • prefix lengths exceeding previous_value.len()
• Other decoders (e.g., DELTA_BINARY_PACKED) perform validation on decoded values,
  but this check is missing here.

Impact

This can cause unexpected panics when reading invalid or unexpected encoded data,
instead of returning a controlled error.