feat: Make num-bigint optional

[fasterthanlime]

Closes #124

Apologies for the few TOML reformats that slipped through, I can get rid of those if needed.

A few statics got turned into consts and moved inline with the BigInt code to avoid "unused variable" warnings.

I would recommend running cargo hack --feature-powerset check in CI, from https://lib.rs/crates/cargo-hack

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A "default features build" (with num-bigint) is 4.7s at best for me:

Command used:

cargo clean ; cargo build --package jiter --quiet --timings && w3m -dump target/*timings/*timing.html | grep 'Total time.*$' --color=always -B3

And a "no default features" build is just under two seconds:

Command used:

cargo clean ; cargo build --package jiter --quiet --timings --no-default-features && w3m -dump target/*timings/*timing.html | grep 'Total time.*$' --color=always -B3

[codspeed-hq[bot]]

CodSpeed Performance Report

Merging #130 will improve performances by 10.75%

_{Comparing bearcove:optional-num-bigint (c611089) with main (dd25fd0)}

Summary

⚡ 1 improvements ✅ 72 untouched benchmarks

Benchmarks breakdown

	Benchmark	main	bearcove:optional-num-bigint	Change
⚡	python_parse_string_array_not_cached	40.1 µs	36.2 µs	+10.75%

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 94.91%. Comparing base (dd25fd0) to head (c611089). Report is 2 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #130   +/-   ##
=======================================
  Coverage   94.91%   94.91%           
=======================================
  Files          12       12           
  Lines        1908     1909    +1     
=======================================
+ Hits         1811     1812    +1     
  Misses         97       97           

Files with missing lines	Coverage Δ
crates/jiter/src/number_decoder.rs	93.26% <100.00%> (+0.02%)	:arrow_up:
crates/jiter/src/value.rs	97.11% <ø> (ø)

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[fasterthanlime]

@fasterthanlime could you rebase please?

Done!

[fasterthanlime]

(Is there a way to "Allow edits by maintainers" after the fact?)

[samuelcolvin]

Thanks so much.

(Is there a way to "Allow edits by maintainers" after the fact?)

I think there might be a way, perhaps a checkbox once if you edit the PR body?

Anyway, happy to merge this once @davidhewitt has a quick check.

[fasterthanlime]

Super, thanks very much!

Thanks for the review+merge! Can you tag me when this lands on crates.io?

(By the way I recommend the excellent release-plz for release automation, in case you're interested)

[cetra3]

I've raised a followup PR for this one as it looks like num-bigint is always pulling in pyo3 as well: https://github.com/pydantic/jiter/pull/160