fix(deps): re-export prometheus

[merklefruit]

users trying to use the metrics macro get a compile error if they don't have prometheus in their workspace:

failed to resolve: use of unresolved module or unlinked crate `prometheus`
if you wanted to use a crate named `prometheus`, use `cargo add prometheus` to add it to your `Cargo.toml`

[thedevbirb]

A procedural macro crate cannot re-export anything other than macros, so I think we've to deal with this. It is already the status quo with a crate like serde. If you want to use serde_derive, you have to import also serde itself.

Or do you mean re-export prometheus from prometric and not prometric-derive?

[merklefruit]

A procedural macro crate cannot re-export anything other than macros, so I think we've to deal with this. It is already the status quo with a crate like serde. If you want to use serde_derive, you have to import also serde itself.

Or do you mean re-export prometheus from prometric and not prometric-derive?

exporting it from prometric should be ok, as the two are never used standalone anyway