change: Add decimal to actual memory usage in proc

[ClementTsang]

Description

A description of the change and what it does. If relevant (such as any change that modifies the UI), please provide screenshots of the change:

This change adds a decimal + single digit to memory usage in the process widget. Note that this only affects all cases where the value is less than 0.05, so we don't have 0.0B displayed. Otherwise, it's a fairly straightforward change.

This change adds a decimal + single digit to memory usage values over the 1 GiB threshold. Otherwise, there is no visible change.

(Note to self: implement the per-column width system soon, this change causes some values to potentially look a bit weird in mem-non-percent mode as it is if the value is really large, like 530.2GiB pushing right up against the column width, but it's currently tied to mem-percent mode. Ugh.)

Also revert a change made by accident where I switched to a decimal prefix system (GB) for memory values. This has been reverted back to a binary prefix (GiB).

Issue

If applicable, what issue does this address?

Closes: #448

Type of change

Remove the irrelevant ones:

• Other (something else - please specify) Small change to add a decimal place to memory usage values

Test methodology

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Furthermore, please tick which platforms this change was tested on:

• Windows
• macOS
• Linux

If relevant, all of these platforms should be tested.

Checklist

If relevant, ensure the following have been met:

• Change has been tested to work, and does not cause new breakage unless intended
• Code has been self-reviewed
• Documentation has been added/updated if needed (README, help menu, etc.)
• Passes CI pipeline (clippy check and cargo test check)
• Areas your change affects have been linted using rustfmt (cargo fmt)
• No merge conflicts arise from the change

Other information

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