Regex.scan with `return: :index` reports BYTE offsets, but String.slice/3
uses CHARACTER offsets. When a record contained a multi-byte UTF-8
character in an earlier field (e.g. "café" in NOTES), every subsequent
field's slice shifted one byte left, eventually landing on a literal
">" that crashed String.to_integer/1 with ArgumentError.
Switch to :binary.part/3 which is byte-based and matches what Regex.scan
reports. Also simplify the value offset calculation to use the scanned
tag_len directly instead of re-splitting the tag text. Reproduced in a
new regression test.
Prod stack trace: AdifImport.parse_fields/1 crashed on upload with
binary_to_integer(">") -- a FreeDV/N1MM logger that embedded UTF-8
characters in a NOTES field triggered it.
Graham McIntire
265669fc3a