Qualify std::time::Duration in proc macros

[lbeschastny]

Using proc macros should not require importing std::time::Duration

Motivation

Apart from just being a good practice, current implementation makes it difficult to use cached in some cases.

For example, I use it like this in one on my projects:

#[cfg_attr(
    not(test),
    cached::proc_macro::once(result = true, sync_writes = true, time = 900)
)]

but after updating cached to 0.56.0 I started getting an error

 1  error[E0433]: failed to resolve: use of undeclared type `Duration`                                                                                                                      ▐                                              ▐
    --> src/edp.rs:126:5                                                                                                                                                                    ▐                                              ▐
     |                                                                                                                                                                                      ▐                                              ▐
 126 |     cached::proc_macro::once(result = true, sync_writes = true, time = 900)
     |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ use of undeclared type `Duration`

and the only way to fix this without getting an unused import warning is to add something like

#[cfg(not(test))]
use std::time::Duration;

which just creates unnecessary complexity.

[lbeschastny]

This condition could be rewritten to look more compact:

match (asyncness.is_some(), time_refresh) {
    (true, Some(time_refresh)) => quote! {
        cached::AsyncRedisCache::new(#cache_prefix, std::time::Duration::from_secs(#time)).set_refresh(#time_refresh).build().await.expect("error constructing AsyncRedisCache in #[io_cached] macro")
    },
    (true, None) => quote! {
        cached::AsyncRedisCache::new(#cache_prefix, std::time::Duration::from_secs(#time)).build().await.expect("error constructing AsyncRedisCache in #[io_cached] macro")
    },
    (false, Some(time_refresh)) => quote! {
        cached::RedisCache::new(#cache_prefix, std::time::Duration::from_secs(#time)).set_refresh(#time_refresh).build().expect("error constructing RedisCache in #[io_cached] macro")
    },
    (false, None) => quote! {
        cached::RedisCache::new(#cache_prefix, std::time::Duration::from_secs(#time)).build().expect("error constructing RedisCache in #[io_cached] macro")
    },
}