Improvement: String error type in Result does not implement std::error::Error

[SeitaHigashi]

Are there any reason about for using String as returning type on any functions?

For example, I found BrowserConfigBuilder.build() returns std::result::Result<BrowserConfig, String>. but String types doesn't implemented std::error:Error. in this implementation, library users can't use any other Result handling library. e.g., anyhow.

If there is no reason about this topic, I'd like to try to update this part. but this updates will become breaking change.

[Sytten]

Happy to get a PR for that, this is worth a breaking change.