Fix warnings about non_local_definitions

[damszew]

This PR changes named constant block to anon-const so rustc doesn't warn about non_local_definitions (and makes minor fixes suggested by clippy)

Details:
Recent nightly versions implement rust-lang/rust#120393 which causes compilation warnings like

warning: non-local `impl` definition, they should be avoided as they go against expectation
 --> src/containers/password.rs:8:38
  |
8 | #[cfg_attr(feature = "pgsql", derive(diesel_derive_newtype::DieselNewType))]
  |                                      ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  |
  = help: move this `impl` block outside the of the current constant `_IMPL_DIESEL_NEW_TYPE_FOR_PASSWORD`
  = note: an `impl` definition is non-local if it is nested inside an item and may impact type checking outside of that item. This can be the case if neither the trait or the self type are at the same nesting level as the `impl`
  = 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 `diesel_derive_newtype::DieselNewType` may come from an old version of the `diesel_derive_newtype` crate, try updating your dependency with `cargo update -p diesel_derive_newtype`
  = note: `#[warn(non_local_definitions)]` on by default
  = note: this warning originates in the derive macro `diesel_derive_newtype::DieselNewType` (in Nightly builds, run with -Z macro-backtrace for more info)

As warning states, this lint might become deny-by-default in the future.
Only exception to this rule are anon-const which are used also by serde to be compatible with different rust editions more info here.

[sfisol]

Hi @quodlibetor, any chance this could be merged any soon?

[quodlibetor]

ah thanks for the ping! And for the fix! yeah I'll get this out.

[quodlibetor]

this is released.