Byte-cursor progress callback for the data-parse loop — the parse phase is
determinate in bytes (cursor position / buffer size). Kept primitive so the
parser stays decoupled from the higher-level progress event contract in
core/progress.ts (ProgressTracker maps this into a ProgressEvent).
Byte-cursor progress callback for the data-parse loop — the parse phase is determinate in bytes (cursor position / buffer size). Kept primitive so the parser stays decoupled from the higher-level progress event contract in core/progress.ts (ProgressTracker maps this into a ProgressEvent).