Replace type aliases with newtypes

[librasn]

Replace type aliases with newtypes

[XAMPPRocky]

Thank you for your issue! This is definitely planned, as I'm currently working on implementing PER and constraints, and constraints I want to eventually move the constraints impl to being completely const based, which requires having our own types to be able to add const parameters.

However, changing the Integer alias to IBig would be a breaking change.

I do want to be clear however that this is acceptable. This crate is still very firmly in 0.x phase of development. So preventing breakage is not priority compared to iterating and improving rasn's features and performance.

Which is a bit jarring when the type signature is named something completely different IMO

Yes, seperately I'd like to be able to massively revamp documentation, to provide more both informative and normative information on ASN.1, such that rasn's documentation is the primaary if not only source you need to use ASN.1 successfully.

[XAMPPRocky]

I am still quite new for Rust, so I might need some design help.

Right now we're mostly limited by Rust's const capabilities, once we have the ability to use enums it will make the design much more intuitive and straightforward.

You can see a simple version of this with the fixed octet string type.

https://github.com/XAMPPRocky/rasn/blob/a7a00c76d702e530a14d517d830adc899bd31dc4/src/types/strings/octet.rs#L7-L8

[Nicceboy]

I think I could start working with this [newtype support] after I finish OER codec, if that is okay.

I am still quite new for Rust, so I might need some design help.

But the basic idea would be to use Crate level features and with that to change types?

For the higher type (Integer) and user facing API, we write our own functions, and then with crate features possibly map to different inner types.