Function parse_line 

pub fn parse_line(line: &str) -> Result<ParsedLine, ParseError>

Fully parse and validate a TSJSON line into a ParsedLine.

Performs all validations including:

• Field count (exactly 8 tab-separated fields)
• wall_ts_us is a valid i64
• agent is non-empty and contains no whitespace
• itc is non-empty
• parents are valid blake3:<payload> hashes (or empty)
• event_type is a known item.<verb>
• item_id is a valid bones ID
• data is valid JSON matching the event type schema
• event_hash is blake3:<payload> and matches the recomputed hash

Errors

Returns ParseError with a specific variant for each validation failure.