Add SHA-512 support

[fghanmi]

Issue #, if available: #813

Description of changes:
Currently only SHA-256 is supported. This PR is going to:

• Implement SHA-512 support alongside the existing SHA-256.
• Ensure backward compatibility with existing systems that rely on SHA-256.

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[jpculp]

Thank you for the contribution! I'm going to get some extra eyes on this as well as your other PR.

[jpculp]

Looks like you're hitting some clippy lints. If you run make build with the latest stable Rust as the default you'll be able to verify locally.

[jpculp]

@fghanmi, would it be possible to include a unit test for this change? We can also have someone on our end take care of it if you'd prefer.

[jku]

The root metadata in tough/tests/data/tuf-sha512/metadata/ is still expiring next month

[jpculp]

Hi @fghanmi. Thank you for your patience on this. I think we're in a good place here. Would you be willing to squash your commits to one for the tough changes and one for tuftool? We can also do it on our end if you would prefer.

[fghanmi]

Hi @fghanmi. Thank you for your patience on this. I think we're in a good place here. Would you be willing to squash your commits to one for the tough changes and one for tuftool? We can also do it on our end if you would prefer.

@jpculp , Thank you!
regarding the squash, I see that the changes on tuftool are only on tuftool/tests/, and one commit does have changes on both tuftool and tough (which is required to have successful tests) - I am really not sure how to organize the commits in this case..

[jpculp]

@fghanmi, that's true. It might make the most sense to keep it as one commit despite it crossing over.

[fghanmi]

@fghanmi, that's true. It might make the most sense to keep it as one commit despite it crossing over.

So squashing to 1 commit is okay ?