test: fix waitTipChanged timeout on slow hosts and use monotonic clock in interface_ipc_mining #36791

Follow up suggested in #36731 (comment).

The first commit fix the timeout on a slow host and the second one use time.monotonic() for durations.

Command to reproduce the errors with a simulated slow wall clock:

faketime --exclude-monotonic -f "+0 x0.1" build/test/functional/interface_ipc_mining.py

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External sites

• Code coverage & benchmarks: https://corecheck.dev/bitcoin/bitcoin/pulls/36791
• Ralph review <img src=https://review.fish.foo/assets/bitcoin/bitcoin/36791.png alt="Ralph review status"> https://git.fish.foo/bitcoin/bitcoin/pulls/36791#author-ralph

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Command to reproduce slow host:

I think this is a "fast host", as the test takes a shorter "wall" time?

Concept ACK

I think this is a "fast host", as the test takes a shorter "wall" time?

You are right. It can be confusing lol. The first commit fixes a wait that takes too long (this is what confused me) and the second fixes durations measured with a wall clock that doesn't match real time. Renamed it to "slow wall clock".

tACK 46ee95db49c9fa7f4b80a1e59816660f5ee0c4f4