Expose physical source line for CSV field-count errors

[osipovartem]

Summary

• Add the one-based physical source line to recoverable CSV field-count errors.
• Reuse the existing source-line counter, including ignored prefixes and multiline records, without adding work to valid-row parsing.
• Cover blank-line and multiline-record positions across decode calls.

Verification

• cargo +1.99.0 test -p arrow-csv --lib (139 passed, 8 ignored)
• cargo +1.99.0 test -p arrow-csv --lib bench_valid_quoted_csv_with_record_handler -- --ignored --nocapture
• Independent read-only review: approved, no blocking findings.

This supports Snowflake-style COPY diagnostics in Rustice; it does not change default CSV error behavior.