Better error handling and reporting

[Seeker14491]

Error handling could use a rework. There's many places in the Rust code where we call unwrap() for things like file system access or downloading stuff, which means Cultivation will crash if any of those operations fail. I think if such an operation fails, we should display that error on the frontend such as with a pop up message. The Rust code will need refactoring first though, so we return Results to the frontend instead of crashing.

[Seeker14491]

I came up with a really simple way to handle errors on the Rust side: https://github.com/Seeker14491/anyhow-tauri. It's just a fork of the popular error handling library anyhow, but with a tiny tweak that lets you return its error type from Tauri commands. As an example, we can rewrite a function like this one in file_helpers.rs:

#[tauri::command]
pub fn read_file(path: String) -> String {
  let path_buf = std::path::PathBuf::from(&path);

  let mut file = match fs::File::open(path_buf) {
    Ok(file) => file,
    Err(e) => {
      println!("Failed to open file: {}", e);
      return String::new();
    }
  };

  let mut contents = String::new();
  file.read_to_string(&mut contents).unwrap();

  contents
}

into this:

#[tauri::command]
pub fn read_file(path: &Path) -> Result<String> {
  let mut file = File::open(path)?;
  let mut contents = String::new();
  file.read_to_string(&mut contents)?;

  Ok(contents)
}

without any other boilerplate. You can also attach context like in vanilla anyhow:

file.read_to_string(&mut contents).context("helpful error context goes here")?;

If the function errors, on the TypeScript side we can read the error and any context it might have. We can also optionally get a backtrace that shows where the error occurred, at least for debug builds.

Also, for file operations specifically, we can use the fs_err crate to get better error messages.