Deny warnings and add miri to CI

[blobcode]

This Pull Request fixes/closes #2366

It changes the following:

• Denies Warnings in cargo build
• Enables miri as a seperate step running on ubuntu (miri has limited support on windows)

Note that this will cause previously passing builds to fail.

[jedel1043]

Opened #2449 to fix the deprecation warnings.

[jedel1043]

Also, I'm not sure if we want to run all tests through MIRI. On my machine (ryzen 5 5600) it takes up to 1hr to run the full test suite. Maybe we should isolate just a couple important tests (JsString, boa_gc, modules using unsafe) and ignore all others on miri runs.

[blobcode]

It looks like according to
rust-lang/miri#1758
we likely will need to add miri to the names of tests we want to run.
If someone could let me know more specifically what tests we want to run through miri to start that would be appreciated.

[jedel1043]

Really sorry for the wait 😅 We'll probably want to just run the tests for JsString and the boa_gc tests, which are the most "unsafe" parts of our engine. Further tests can be added to the list as we add them to the repo.

We think it should be better to exclude whole modules from miri runs using #[cfg_attr(miri, ignore)], since it saves us the pain of categorizing tests individually.