fix: use anon-const for wrapping expanded impls

[shekhirin]

On latest nightly, with the introduction of https://github.com/rust-lang/rust/issues/120363, proptest derives don't pass lints anymore, e.g.

error: non-local `impl` definition, they should be avoided as they go against expectation
  --> crates/primitives/src/account.rs:15:12
   |
15 | pub struct Account {
   |            ^^^^^^^
   |
   = help: move this `impl` block outside the of the current constant `_IMPL_ARBITRARY_FOR_Account`
   = note: an `impl` definition is non-local if it is nested inside an item and neither the type nor the trait are at the same nesting level as the `impl` block
   = note: one exception to the rule are anon-const (`const _: () = { ... }`) at top-level module and anon-const at the same nesting as the trait or type
   = note: this lint may become deny-by-default in the edition 2024 and higher, see the tracking issue <https://github.com/rust-lang/rust/issues/120363>
   = note: the derive macro `AccountPropTestArbitrary` may come from an old version of the `proptest_derive` crate, try updating your dependency with `cargo update -p proptest_derive`
   = note: `-D non-local-definitions` implied by `-D warnings`
   = help: to override `-D warnings` add `#[allow(non_local_definitions)]`
   = note: this error originates in the derive macro `AccountPropTestArbitrary` (in Nightly builds, run with -Z macro-backtrace for more info)

This fix is similar to https://github.com/dtolnay/typetag/commit/d51f4adc253f12a02939625ebbab9305ca66f567, i.e. use anon const expressions instead of named ones.

[shekhirin]

@matthew-russo PTAL when you have time, as it blocks nightly CIs on projects like Reth (https://github.com/paradigmxyz/reth/actions/runs/8048254493/job/21979197918)

[matthew-russo]

@shekhirin

looks like nightly has failing unit tests https://github.com/proptest-rs/proptest/actions/runs/8048322898/job/22017111787?pr=427#step:13:770

i'll try to give a look one evening this week. if you get to it first, let me know

[shekhirin]

@matthew-russo ah, it's an easy one, fixed! Can you please re-run the CI?

[matthew-russo]

Thanks, I'll try to cut a release this week as we have a couple fixes pending

[DaniPopes]

Hey @matthew-russo, any updates on this? I saw proptest was released but not proptest-derive, was this missed? Thanks!

[matthew-russo]

Sorry I had to take some time away to deal with projects at home. I'll be triaging issues this week and throw cutting a derive release in there as well