remove cow and add concurrent upload/save

[BJSummerfield]

Use static str for devices

Cow adds unnecessary overhead. We are creating and returning static strings with devices, never using the Owned enum variant. With Cow, each device creates an enum that holds references to an Owned memory location and/or a Borrowed memory location. However, this program only uses Borrowed path.

Removing the overhead creates a small but measurable improvement.

Local stress test using Cow running wrk -t12 -c400 -d30s http://localhost:8080/api/devices Requests/sec: 171901.99 172399.36 172104.08

Using static strings Requests/sec: 173199.04 173038.07 172948.25

Image save and upload concurrently

No need to wait for image upload to happen before save (unless we want to). Run them both at the same time with tokio::join

[antonputra]

Thanks @BJSummerfield for the PR, let me test it and I'll merge

[antonputra]

What do you think? @devashishdxt

[devashishdxt]

Using &'a str is definitely better than using Cow. I also thought of this but decided not to do that because in a real world application, you rarely return static strings which are known at compile time.

For concurrently saving and uploading, you'll also have to make changes in go application so that go executes both in parallel. Doing it concurrently will be faster in both the languages.

[antonputra]

Thanks, i'll update go code before the next test!