Added additional unit flexibility for download/upload speeds.

[Windows81]

When it comes to measuring internet speeds, I like to have all my units in mebibytes/second, as this is how both OS-level file managers and web browsers would display object sizes and download speeds. Although speedtest-cli allow speeds to be displayed in megabytes/second, having a multiplication factor of 1.048576 makes it inconvenient for when you happen to be comparing similar test results that may have happened to come from outside sources. As with Okla, I've also added other units too!

I should also disclose that this is my first time contributing to open-source software.

[maulanaaghnii]

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[Windows81]

Hello @sivel. I wanted to follow up with this pull request. Please review the changes at your earliest convenience. Thanks in advance for the merge!

[Windows81]

Hey. Just wanted to follow up once again. The utility already works on Python 3.12, but I replaced datetime.datetime.utcnow() with datetime.datetime.now(datetime.UTC), as per the deprecation warning.