Replace backtrace fields on wrapper error types with methods

[data-sync-user]

We are doing a lot of cloneing of the backtraces we generate in inner error types when converting Kinds into their wrapper types in From impls. If this proves to have substantial performance implications, we should replace the backtrace fields on the outer types with methods that return a reference to the backtrace fields on the wrapped “kind” types.

For example, we might have a type ApiErrorKind that looks something like

struct ApiErrorKind {
    ...
    backtrace: Backtrace,
    ...
}

and a wrapper type ApiError that looks like

struct ApiError {
    ...
    kind: ApiErrorKind,
    backtrace: Backtrace,
    ...
}

where the backtrace field in ApiError is a clone of the backtrace field in ApiErrorKind. Instead of cloning that field, we could implement a method on ApiError like so:

impl ApiError {
    fn backtrace(&self) -> &Backtrace {
        &self.kind.backtrace
    }
}

┆Issue is synchronized with this Jira Task