perf(toml): Allow opting in to faster hasher

[epage]

I chose foldhash because it is the default of [email protected] (replacing ahash), see rust-lang/hashbrown#563.

Currently, ahash is the only hasher I noticed inside of Cargo and that is coming in from [email protected].

In the future, we could consider allowing the use of a FixedState so we could offer IndexMap on alloc.

$ cargo bench --bench 0-cargo -Fpreserve_order -- 0_cargo::toml::document::2-features
   Compiling toml v0.5.11
   Compiling toml v0.8.23 (/home/epage/src/personal/toml/crates/toml)
   Compiling toml_benchmarks v0.0.0 (/home/epage/src/personal/toml/crates/benchmarks)
    Finished `bench` profile [optimized] target(s) in 19.13s
     Running benches/0-cargo.rs (/home/epage/src/personal/toml/target/release/deps/0_cargo-09d7e00849b1b878)
Timer precision: 11 ns
0_cargo              fastest       │ slowest       │ median        │ mean          │ samples │ iters
╰─ toml                            │               │               │               │         │
   ╰─ document                     │               │               │               │         │
      ╰─ 2-features  468.8 µs      │ 1.016 ms      │ 513.5 µs      │ 543.5 µs      │ 100     │ 100


$ cargo bench --bench 0-cargo -Ffast_hash -- 0_cargo::toml::document::2-features
    Finished `bench` profile [optimized] target(s) in 0.02s
     Running benches/0-cargo.rs (/home/epage/src/personal/toml/target/release/deps/0_cargo-ea11bd9a52599c35)
Timer precision: 18 ns
0_cargo              fastest       │ slowest       │ median        │ mean          │ samples │ iters
╰─ toml                            │               │               │               │         │
   ╰─ document                     │               │               │               │         │
      ╰─ 2-features  431.4 µs      │ 870.3 µs      │ 446.2 µs      │ 459.9 µs      │ 100     │ 100

[coveralls]

Pull Request Test Coverage Report for Build 15690907547

Details

• 3 of 4 (75.0%) changed or added relevant lines in 1 file are covered.
• 1 unchanged line in 1 file lost coverage.
• Overall coverage decreased (-0.008%) to 69.303%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
crates/toml/src/map.rs	3	4	75.0%

Files with Coverage Reduction	New Missed Lines	%
crates/toml/src/map.rs	1	66.15%

Totals
Change from base Build 15687156076:	-0.008%
Covered Lines:	6204
Relevant Lines:	8952

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💛 - Coveralls