bug: forgot to create memory usage string when collapsed

[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:

Adds a line to actually build the string of the summed memory usage. I forgot to make the string after summing the values.

Before:

After:

Issue

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Closes: #

Type of change

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• Bug fix (non-breaking change which fixes an issue)

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Checklist

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• 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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