Fix: Graph deleted before aptly exits

[reglim]

Fixes: #1213

Requirements

All new code should be covered with tests, documentation should be updated. CI should pass.

Description of the Change

The temporary output file is now only deleted after copying it to the output location. We no longer wait 1s for the open command, but exit immediately, since the process will continue running even after aptly exits.

Why this change is important?

Because the assumption was made that any application that opened the image would continue displaying it, even if the image was removed right after, which isn't true for the Gnome Image Viewer.

Checklist

• [ ] unit-test added (if change is algorithm)
• [ ] functional test added/updated (if change is functional)
• [ ] man page updated (if applicable)
• [ ] bash completion updated (if applicable)
• [ ] documentation updated
• [x] author name in AUTHORS

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 18.18182% with 9 lines in your changes missing coverage. Please review.

Project coverage is 66.64%. Comparing base (4bc2180) to head (7192f1e).

:exclamation: Current head 7192f1e differs from pull request most recent head 33fe7de

Please upload reports for the commit 33fe7de to get more accurate results.

Files	Patch %	Lines
cmd/graph.go	18.18%	9 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #1214 +/- ## ========================================== - Coverage 74.81% 66.64% -8.17% ========================================== Files 144 143 -1 Lines 16248 16184 -64 ========================================== - Hits 12156 10786 -1370 - Misses 3152 4630 +1478 + Partials 940 768 -172 ```

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