feat(timers): Implement drop-in replacement of `futures_timer::Delay`

[oblique]

Description

In some cases a compatibility layer with futures-timer is needed. This PR add a drop-in replacement for futures_timer::Delay.

How Has This Been Tested?

Started a local node and tested a simple call to ic_cdk_timers::Delay.

Checklist:

• [x] The title of this PR complies with Conventional Commits.
• [x] I have edited the CHANGELOG accordingly.
• [x] I have made corresponding changes to the documentation.

[dfinity-droid-prod[bot]]

Dear @oblique,

In order to potentially merge your code in this open-source repository and therefore proceed with your contribution, we need to have your approval on DFINITY's CLA[^1].

If you decide to agree with it, please visit this issue and read the instructions there.

— The DFINITY Foundation [^1]: Contributor License Agreement