Allow configuration of receive timeout for assert_*, and refute_* functions

[validere-ben]

Context

We're currently running into issues with intermittent test failures in certain environments due to the hardcoded 100ms receive timeout on these test assertions.

Judging from #228 100ms being hardcoded seems quite arbitrary?

Suggestions

Having a :timeout opt be added to these functions or adding /2 variants allowing a timeout specification would be a welcome extension.

There is also the existing refute_timeout configuration option which seems to only be used with assert_no_emails_delivered/0 currently (should refute_email_delivered_with/1 be using this as well?). Following this existing convention, an assert_timeout 'global' configuration option might be more suitable?

I'd be happy to cut a PR with the changes depending on the approach/solution preferred for this.

[germsvel]

Hi @validere-ben. Thank you for opening up this issue, and thanks for the patience! I think it'd be a great idea to make that timeout configurable by passing a timeout option. We can just keep 100ms as the default. I know it's been a while since you opened this issue, but if you're interested, I'd review a PR for this. Otherwise, thanks for the idea. Maybe someone else will come along and be interested in taking this.