Run Miri and fix issues

[Wodann]

• [x] claim this issue (assign yourself or comment below)
• [ ] setup repository on your local machine and make sure all tests pass (cargo test)
• [ ] read our contributing guidelines
• [ ] run Miri on the mun codebase
• [ ] fix all errors and warnings reported by Miri
• [ ] (BONUS) add a ci job for running Miri
• [ ] start a Pull Request. Set description to closes #420. If this is your first PR, welcome :tada: :smile:

[belagoesr]

I'll be taking this one!