feat: impl Error for TryFromError

[dannyhammer]

This implements the error::Error trait on the TryFromError enum.

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The only other error type in uom is ParseQuantityError, which already implements Error. I copied the same structure for implementing Error on this type, modifying the error messages appropriately.

The reason I am proposing this change is because I recently found myself wanting to write a function like this:

fn uom_time_str_to_std_duration(s: &str) -> anyhow::Result<std::time::Duration> {
    let time: uom::si::f64::Time = s.parse()?;
    let duration = time.try_into()?;
    Ok(duration)
}

However, this function does not compile, and results in the following error:

error[E0277]: the trait bound `TryFromError: std::error::Error` is not satisfied
  --> src/main.rs:15:35
   |
15 |     let duration = time.try_into()?;
   |                                   ^ the trait `std::error::Error` is not implemented for `TryFromError`, which is required by `Result<Duration, anyhow::Error>: FromResidual<Result<Infallible, _>>`
   |
   = help: the trait `FromResidual<Result<Infallible, E>>` is implemented for `Result<T, F>`
   = note: required for `anyhow::Error` to implement `From<TryFromError>`
   = note: required for `Result<Duration, anyhow::Error>` to implement `FromResidual<Result<Infallible, TryFromError>>`

For more information about this error, try `rustc --explain E0277`.

This PR resolves this issue.

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This is my first contribution to uom, so if I have missed anything important, please let me know.