Code Quality: HashesViewModel and ChecksumHelpers can be improved

[KrisVandermotten]

Description

In #18073 we fixed #18069.

Those same fixes should be applied to HashesViewModel.CalculateFileHashAsync and the ChecksumHelpers methods.

Additionally, in HashesViewModel.CalculateFileHashAsync, we should open and close the stream on the background thread we're using to hash it.

Concerned code

• src\Files.App\ViewModels\Properties\HashesViewModel.cs
• src\Files.Shared\Helpers\ChecksumHelpers.cs

Gains

• Better readability.
• Consistency.
• Better performance (event though virtually unnoticeable).

Requirements

• Use MD5.HashData method in HashesViewModel.CalculateFileHashAsync.
• Use Convert.ToHexStringLower.

Comments

I have a PR, I'll take the liberty of sending it.

[yair100]

Sounds good 👍