perf: Bump foldhash to 0.2.0

[hoxxep]

Following up from the rapidhash PR #633, this bumps foldhash to 0.2.0 for a large improvement in foldhash's string hashing.

Both rapidhash and foldhash are equal in the hashbrown benchmark suite as it only tests the hashing of usize objects.

The reason foldhash 0.2.0 required a major version bump is because FoldHasher now has a lifetime parameter. I don't know how users are expected to use DefaultHashBuilder, but noting that it likely makes this a breaking change for hashbrown?

cc. @orlp @Amanieu from #633

[orlp]

I'm not sure if it's a breaking release, the DefaultHashBuilder still implements the HashBuilder contract all the same, and that lifetime is just 'static on an associated type.

[CryZe]

I believe it technically is breaking because you could pass DefaultHashBuilder to a function expecting foldhash-0.1::RandomState whereas that breaks with this. DefaultHashBuilder probably should be using the newtype pattern.

[jqnatividad]

FYI... I also got this compilation error when I attempted to use this PR on [patch.crates-io] of my project's Cargo.toml

error[E0204]: the trait `core::marker::Copy` cannot be implemented for this type
  --> /Users/jdoe/.cargo/registry/src/index.crates.io-1949cf8c6b5b557f/hashlink-0.10.0/src/lib.rs:19:17
   |
19 | #[derive(Clone, Copy, Default, Debug)]
   |                 ^^^^
20 | pub struct DefaultHashBuilder(hashbrown::DefaultHashBuilder);
   |                               ----------------------------- this field does not implement `core::marker::Copy`

[cuviper]

DefaultHashBuilder probably should be using the newtype pattern.

Yes -- this might be a good time to do that and bump to 0.16.

[orlp]

FYI... I also got this compilation error when I attempted to use this PR on [patch.crates-io] of my project's Cargo.toml

error[E0204]: the trait `core::marker::Copy` cannot be implemented for this type
  --> /Users/jdoe/.cargo/registry/src/index.crates.io-1949cf8c6b5b557f/hashlink-0.10.0/src/lib.rs:19:17
   |
19 | #[derive(Clone, Copy, Default, Debug)]
   |                 ^^^^
20 | pub struct DefaultHashBuilder(hashbrown::DefaultHashBuilder);
   |                               ----------------------------- this field does not implement `core::marker::Copy`

See here for context: orlp/foldhash#28.

But yes, the lack of a newtype pattern meant that this breaking change would leak into hashbrown as it directly passes through any traits that were implemented.

[cuviper]

See #643 for a newtype.