Easy: Resolve Clippy

[bh2smith]

Motivation

Just getting started with the project and wanted to satisfy clippy before I dive in.

Solution

Addressed all clippy warnings in a single commit.

1. Most were just removing return from thrown errors in favour of rust's inferred return.
2. Changed some iterator.len() == 0 comparisons for iterator.is_empty().
3. There was one warning regarding the use of .last().

warning: called `Iterator::last` on a `DoubleEndedIterator`; this will needlessly iterate the entire iterator
  --> crates/cli/src/parse/timestamps.rs:26:17
   |
26 | /                 path.split(':')
27 | |                     .last()
   | |______________________-----^
   |                        |
   |                        help: try: `next_back()`
   |
   = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#double_ended_iterator_last

PR Checklist

Existing tests should cover the bases here. No need for additional docs and are not expected to introduce any breaking changes.

• Added Tests
• Added Documentation
• Breaking changes