refactor: show finding in problems panel on single line

[6d7a]

Context

Currently, we display a detailed, multi-line message for each secret we find in VSCode's Problems View. The Problems View lists all issues raised from installed extensions by file. By convention, the individual problem message should spawn only one line.

What has been done

This PR shortens the result of a ggshield scan to one line per finding. The full finding data remains visible through the hover window.

Validation

• run the extension
• open a repository that contains an inline secret detected by ggshield
• open the Problems View
• ensure that the secret issue is summarized in a single line

PR check list

• As much as possible, the changes include tests
• If the changes affect the end user (new feature, behavior change, bug fix) then the PR has a changelog entry.