Add bounds checks to JSON Lines array iterator

[SRO-SA]

Fixes #5

Summary:

• Adds bounds checks before JSON Lines iterator traversal reads structural-array entries.
• Validates node, nextNode, pair_pos, and structural-derived file positions before access.
• Avoids mutating iterator state until the requested array index is confirmed valid.
• Rejects negative indexes and empty-array accesses.

Testing:

• I could not run the ASAN reproducer locally because my laptop does not have CUDA access.
• I reviewed the affected host-side iterator traversal manually.
• Please rerun the ASAN reproducer from the issue to confirm the heap-buffer-overflow is resolved.