Instead of requiring downstream consumers to re-derive the byte offset
from pointer arithmetic on the Highlight slice, compute and cache the
offset inside the parser at error-capture time via setErrOffset().
This is safer because:
- The parser is the one place where the backing-array guarantee is known
to hold (Highlight is always a subslice of the parse buffer)
- Downstream consumers (wrapDecodeError) can use the cached offset
directly, avoiding the need for pointer comparison
- Errors created outside the parser (strict.go) set the offset from
existing Raw ranges, which are already correct by construction
Add ParserError.SetOffset/Offset methods for setting and retrieving the
cached offset. Update wrapDecodeError to prefer the cached offset when
available, falling back to subsliceOffset for backward compatibility.
Co-authored-by: Thomas Pelletier <thomas@pelletier.dev>
Cursor Agent
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