chore: unused deps

[jdockerty]

After running the udeps command, these were the unused dependencies for the project.

cargo +nightly udeps --all-targets
    Checking gruglb v0.1.0 (/home/influx/work/gruglb)
    Finished dev [unoptimized + debuginfo] target(s) in 4.40s
unused dependencies:
`gruglb v0.1.0 (/home/influx/work/gruglb)`
└─── dependencies
     ├─── "rand"
     ├─── "serde_json"
     └─── "thiserror"
Note: They might be false-positive.
      For example, `cargo-udeps` cannot detect usage of crates that are only used in doc-tests.
      To ignore some dependencies, write `package.metadata.cargo-udeps.ignore` in Cargo.toml.

The tests still pass, which should ensure that they are not used in its core functionality and are safe to remove. I did a small manual test as well and that supports this conclusion too.