ratelimit: add method to retrieve the next refill time

[cgzones]

Useful to check whether the rate limiter has been is use in the recent past, e.g. to drop obsolete per client rate limiters.

p.s.:

cargo clippy currently fails for me due to:

error: written amount is not handled
   --> awaken/src/lib.rs:103:19
    |
103 |             match (&self.inner).write(&[1, 0, 0, 0, 0, 0, 0, 0]) {
    |                   ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    |
    = help: use `Write::write_all` instead, or handle partial writes
note: the result is consumed here, but the amount of I/O bytes remains unhandled
   --> awaken/src/lib.rs:104:17
    |
104 |                 Ok(_) => Ok(()),
    |                 ^^^^^
    = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#unused_io_amount
    = note: `#[deny(clippy::unused_io_amount)]` on by default

error: written amount is not handled
   --> awaken/src/lib.rs:119:19
    |
119 |             match (&self.inner).write(&[0, 0, 0, 0, 0, 0, 0, 0]) {
    |                   ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    |
    = help: use `Write::write_all` instead, or handle partial writes
note: the result is consumed here, but the amount of I/O bytes remains unhandled
   --> awaken/src/lib.rs:120:17
    |
120 |                 Ok(_) => Ok(()),
    |                 ^^^^^
    = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#unused_io_amount

error: could not compile `awaken` (lib) due to 2 previous errors

[brayniac]

Thanks for opening this. I think this is a good addition. I'll open a separate issue for the clippy failures in awaken.

I'll cut a release after test complete and this is merged. Thank you again!

[brayniac]

LGTM. Thank you!

[brayniac]

This is included in ratelimit v0.10.0 which is now live on crates.io. We appreciate the contribution!