Add `inspect` and `inspect_err` to `Result` and `Option`

[gibbz00]

Reference:

• https://doc.rust-lang.org/std/result/enum.Result.html#method.inspect
• https://doc.rust-lang.org/std/result/enum.Result.html#method.inspect_err
• https://doc.rust-lang.org/std/option/enum.Option.html#method.inspect

Unfortunately, I don't have the time to send in a PR right now. Maybe in the future.