Support running inside miri

[ryoqun]

hi :)

As the title just says, this pr adds minimal support for running under miri.

I wonder this pr could be merged without much hassle from me like enhancing ci... ;)

[oconnor663]

Thanks! I've followed up with 2435e29 and d57818a to get cargo +nightly miri test working. It takes forever though, so I probably won't add it to CI 😅

[oconnor663]

CI integration: 5b9af1c

[ryoqun]

@oconnor663 hey, really thanks for polishing the miri support. now that it's minimally covered even by ci, i have to ask you: why not 1.5.1? :) Thanks in advance.

[oconnor663]

Good call, done.