feat: use a clock interface to better support testing for pstoremem

[MarcoPolo]

Necessary to fix some of the flaky tests in go-libp2p. For example libp2p/go-libp2p#1523 is flaky because we assume that right after we disconnect a peer and check the addrs less than 500ms has elapsed. Of course in a normal environment that's a fine assumption, but in these CI environments relying on things generally happening in a certain amount of time leads to flaky test results.

This also has the added benefit that things don't have to sleep to test the passage of time, they can increment the mock clock. (Didn't update the test suite since I didn't want to update pstoreds version).

[marten-seemann]

This also has the added benefit that things don't have to sleep to test the passage of time, they can increment the mock clock. (Didn't update the test suite since I didn't want to update pstoreds version).

We probably should do this, if we want to consolidate this repo as well (libp2p/go-libp2p#1556). Doesn't need to be in this PR though.