Add new_unchecked API

[stefano-garzarella]

In some scenarios we cannot use cpuid (e.g. for now in Coconut SVSM) or we want to force the use of rdrand and rdseed, so let's provide a new unsafe constructor.

[nagisa]

Is Coconut SVSM not its own target? For SGX we’ve adjusted plain fn new to not make any checks, but regardless I think it isn’t a terrible idea to provide an unchecked method.

[stefano-garzarella]

Is Coconut SVSM not its own target?

I'm not sure if I get it.
Coconut SVSM is almost a firmware, e.g. we are using x86_64-unknown-none to build it. So I suppose it does not have its own target.

For SGX we’ve adjusted plain fn new to not make any checks,

Oh I see, IIUC in our case target_env is "".

but regardless I think it isn’t a terrible idea to provide an unchecked method.

Yeah, thanks!

[stefano-garzarella]

@nagisa I updated this PR with your suggestions, please let me know if it is fine to be merged.

FYI I'll be off from Dec 18 to Jan 1.

[nagisa]

Published as 0.8.3