VariantUtil.getMetadataMap reads from wrong position for non-array ByteBuffer; VariantBuilder.appendBinary mutates caller's ByteBuffer

[rayokota]

Describe the bug, including details regarding any error messages, version, and platform.

Description:

• getMetadataMap incorrect position

  In VariantUtil.getMetadataMap, the else-branch (read-only or non-array-backed
  ByteBuffer) computes the slice position incorrectly:

  slice(metadata, stringStart + offset)
  

  stringStart is relative to pos (metadata.position()), but the array-backed
  branch correctly adds pos:

  metadata.arrayOffset() + pos + stringStart + offset
  

  This causes incorrect dictionary parsing or exceptions when the metadata
  ByteBuffer has a non-zero position (e.g., when it is a slice of a larger buffer).

  The sibling method getMetadataKey does not have this bug because dataPos is
  computed as an absolute position.

• appendBinary mutates caller's ByteBuffer

  VariantBuilder.appendBinary(ByteBuffer) calls .put(binary) which advances the
  caller's ByteBuffer position. The analogous method appendEncodedValue uses
  value.duplicate().get(...) to avoid this side effect.

Component(s)

Core