Improve line, col calculate performance by use move cursor on Pairs Iterator.

[huacnlee]

ref: #707, #560

This implementation is based by I use in AutoCorrect: https://github.com/huacnlee/autocorrect/blob/v2.5.5/autocorrect/src/result.rs#L267

Add line_col method for get (line, col) in pair

let mut pairs = JSONParser::parse(Rule::a, "....").unwrap();
let pair = pairs.next().unwrap();
let (line, col) = pair.line_col()

In this method, line, col has managed by move_cursor on Pairs iterator next method. For a large input string this method will be faster, because it does not need to re-calculate all of the input string. The line, col value has been cached in the pair and accumulate by next method.

And I keep the old line_col method in Position struct, because I found that has been used in other without Pairs iterator. This method still works, but it will be slower than the new method.

Benchmark

pair.line_col                              time:   [2.9937 µs 2.9975 µs 3.0018 µs]
position.line_col                          time:   [212.59 µs 213.38 µs 214.29 µs]
position.line_col (with fast-line-col)     time:   [18.241 µs 18.382 µs 18.655 µs]

🎊 9x fast than position.line_col with fast-line-col
🌈 100x fast than old position.line_col

Limitation

This implementation only work for forward iteration for Pairs. So iterate backward will fallback to Position::line_col method.

[tomtau]

one alternative for testing may be a different test parser definition, plus check that position and pair results match ?

btw is there a need for fast-line-col with this, or should that feature be removed? @huacnlee @NoahTheDuke

[huacnlee]

We still need fast-line-col, because my implementation only work for call from Pairs.

There have many case use Position in directly.

[huacnlee]

Hi @tomtau

I have done all, please review again.