feat: box all errors, implement send sync

[xhyrom]

related EFForg/tokio-dl-stream-to-disk#4

Sorry for committing the git part, i can remove it if you want to accept this. This will allow using this library in web frameworks like warp that requires thread-safety errors. Now, it throws:

rustc: `dyn StdError` cannot be sent between threads safely
the trait `Send` is not implemented for `dyn StdError`, which is required by `impl Future<Output = Result<impl Reply, Rejection>>: Send`
required for `Unique<dyn StdError>` to implement `Send`
the full name for the type has been written to '/home/hyro/Workspace/distroid/target/debug/deps/distroid-3a33c2c6c4999731.long-type-1970017503322297020.txt'
consider using `--verbose` to print the full type name to the console
the full name for the type has been written to '/home/hyro/Workspace/distroid/target/debug/deps/distroid-3a33c2c6c4999731.long-type-12577559284257743472.txt'
consider using `--verbose` to print the full type name to the console

also with axum.