feature request: add optional support for the ryu crate to speed up writing numeric worksheet data

Add a Cargo.toml feature to optionally use the ryu crate to speed up writing worksheet numeric data.

This has a positive effect when writing large numeric data sets. Specifically it has a benefit when writing more than 300,000 numeric data cells and when writing 5,000,000 numeric cells it can be 30% faster. See the table below.

Number of cells	Ryu/Standard
100,000	95%
300,000	100%
500,000	105%
750,000	110%
1,000,000	114%
2,000,000	124%
3,000,000	127%
4,000,000	129%
5,000,000	131%

Excel chart

The benchmark was run using the following program:


use rust_xlsxwriter::{Workbook, XlsxError};
use std::env;

fn main() -> Result<(), XlsxError> {
    let args: Vec<String> = env::args().collect();

    let mut workbook = Workbook::new();

    let col_max = 50;
    let mut row_max = match args.get(1) {
        Some(arg) => arg.parse::<u32>().unwrap_or(4_000),
        None => 4_000,
    };

    row_max /= 50;

    let worksheet = workbook.add_worksheet();

    for row in 0..row_max {
        for col in 0..col_max {
            worksheet.write_number(row, col, 12345.0)?;
        }
    }

    workbook.save("rust_perf_test.xlsx")?;

    Ok(())
}

The benchmarking was run with hyperfine:

$ hyperfine --warmup 3 "./app_perf_test4_orig 5000000" "./app_perf_test4_ryu 5000000"
Benchmark 1: ./app_perf_test4_orig 5000000
  Time (mean ± σ):      5.859 s ±  0.061 s    [User: 5.528 s, System: 0.306 s]
  Range (min … max):    5.767 s …  5.946 s    10 runs

Benchmark 2: ./app_perf_test4_ryu 5000000
  Time (mean ± σ):      4.462 s ±  0.035 s    [User: 4.150 s, System: 0.298 s]
  Range (min … max):    4.414 s …  4.523 s    10 runs

Summary
  ./app_perf_test4_ryu 5000000 ran
1.31 ± 0.02 times faster than ./app_perf_test4_orig 5000000

The change was only added to the worksheet number cell writing code since that is the only part of the inner loop where it would have a substantive effect.

jmcnamara / rust_xlsxwriter

feature request: add optional support for the ryu crate to speed up writing numeric worksheet data #93