perf: Refactor CSV serialization to not go thorough AnyValue

[ChayimFriedman2]

While convenient, this harms performance. Avoiding it gives a boost of 40% on my machine, and even more if I limit to single thread.

I did several other things to improve performance, like pre-compilation of date/time formatting and speeding up strings with quotes that need to be escaped. Those aren't strictly related, but they are nice.

Benchmark (the POOL.install() is because otherwise the switch to Polars' pool has a measurable overhead, but this should be only present in benchmarking and not in real-world cases):

use criterion::{black_box, criterion_group, criterion_main, Criterion};
use mimalloc::MiMalloc;
use polars::prelude::*;
use polars_core::POOL;

#[global_allocator]
static MIMALLOC: MiMalloc = MiMalloc;

fn my_benchmark(_c: &mut Criterion) {
    POOL.install(|| {
        let mut c = Criterion::default().configure_from_args();
        const SIZE: i32 = 10_000;
        let mut df = df![
            "a" => (0..SIZE).collect::<Vec<_>>(),
            "b" => (0..SIZE).map(|v| v.to_string()).collect::<Vec<_>>(),
        ]
        .unwrap();

        let mut csv = Vec::new();
        c.bench_function("CSV serialization", |b| {
            b.iter(|| {
                csv.clear();
                CsvWriter::new(&mut csv).finish(&mut df).unwrap();
                black_box(&csv);
            })
        });
    });
}

criterion_group!(benches, my_benchmark);
criterion_main!(benches);

[codecov]

Codecov Report

Attention: Patch coverage is 95.30387% with 34 lines in your changes are missing coverage. Please review.

Project coverage is 81.19%. Comparing base (97c61fe) to head (2388a22).
Report is 10 commits behind head on main.

Files	Patch %	Lines
crates/polars-io/src/csv/write_impl/serializer.rs	96.33%	19 Missing ⚠️
crates/polars-io/src/csv/write_impl/mod.rs	92.71%	15 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #15576      +/-   ##
==========================================
+ Coverage   81.08%   81.19%   +0.11%     
==========================================
  Files        1367     1368       +1     
  Lines      174872   175289     +417     
  Branches     2530     2530              
==========================================
+ Hits       141799   142333     +534     
+ Misses      32598    32482     -116     
+ Partials      475      474       -1     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

[codspeed-hq]

CodSpeed Performance Report

Merging #15576 will not alter performance

_{Comparing ChayimFriedman2:speedup-csv-writer (2388a22) with main (05d980f)}

Summary

✅ 22 untouched benchmarks

[ritchie46]

Thanks for the PR. This certainly looks interesting. Will take a look tomorrow.

[ritchie46]

I went through this carefully and this looks great! 🙌 Really neat monomorphization and constant usage to ensure we get an optimal serializer. Thanks a lot.