Function influxdb_line_protocol::split_lines

pub fn split_lines(input: &str) -> impl Iterator<Item = &str>

Split input into individual lines to be parsed, based on the rules of the line protocol format.

This code is more or less a direct port of the Go implementation of scanLine

While this choice of implementation definitely means there is logic duplication for scanning fields, duplicating it also means we can be more sure of the compatibility of the Rust parser and the canonical Go parser.