Add StorageIndex newtype

[sistemd]

In our database, every trie node has a unique storage index. We simply represent this as a u64 in the code. The code would be a bit clearer and a bit less error prone if we had a simple newtype for it.

[varun-doshi]

I can take this up if its still open

[0xdevcollins]

May I pick this up?

[mimisavage]

Could I be assigned to this?

[vbar]

Could I be assigned to this?

It's already being implemented, in #2428 .

[aidenwong812]

Can I take care of this issue?

[JuViquez]

Hi, I'm new to Only Dust and actively looking to start contributing to this community. If you think this is a good issue for a newbie in web3, I'll gladly help.