Add leading colon to `ts_rs` path in macro expansion

[escritorio-gustavo]

Goal

If, for some (very bespoke and cursed) reason, a user creates a mod called ts_rs and has it in scope, it becomes impossible to derive TS, all the ts_rs::<something> paths will look inside that mod instead of our library. This PR aims to make such (cursed) code compile

Changes

All paths to ts_rs generated by ts_rs_macros now have two leading colons, e.g.: ::ts_rs::TS

Checklist

• [x] I have followed the steps listed in the Contributing guide.
• [x] I have added or updated the tests related to the changes made.