Decide How a Signal-Killed Repair Run Affects DeleteInvalidFiles #1095

Behavior

A signal-ended FfMpeg verify run is recorded in ToolErrorScope.SignalCount, so DeleteFailedFile() keeps the file and a failed repair leaves its state unchanged. The repair runs themselves are not covered. FfMpegTool.ConvertToMkv(), the FfMpeg re-encode, and HandBrakeTool.ConvertToMkv() run with CommandResultValidation.None, so a run killed by a signal reports as executed with a non-zero exit, and the repair tier just fails.

1. A verify finds a genuine decode error, for example FFmpeg exit 183 for invalid data.
2. The remux tier fails, then the FfMpeg re-encode is killed by a signal, for example by the out-of-memory killer during a long encode, and HandBrake fails or is killed too.
3. VerifyAndRepair() sets VerifyFailed and RepairFailed, and with DeleteInvalidFiles on, DeleteFailedFile() deletes the file, although the repair never ran to a result.

This predates the change for #1090, which covers only the verify run. CodeRabbit raised it on #1093.

Reproduction shape

1. Set Verify: true, AutoRepair: true and DeleteInvalidFiles: true.
2. Process a file whose verify reports a decode error, and kill the FfMpeg re-encode with SIGKILL while it runs.
3. The file ends VerifyFailed and RepairFailed, and it is deleted.

The decision

1. Treat a signal-ended repair run as a tool that did not run. Record it in ToolErrorScope.Count, so the failed repair leaves the state unchanged and the file is kept, and the next run repairs again. A repair that crashes on the same input every time re-runs on every run.
2. Treat it like the signal-ended verify. Record it in SignalCount, which keeps the file and also leaves the state unchanged, the same outcome as choice 1 through the Decide How a Signal-Terminated FfMpeg Verify Run Is Classified #1090 path.
3. Keep the current behavior. The verify already judged the media corrupt, so a killed repair still ends in a delete.

Choices 1 and 2 differ only in which count carries it. The question is whether a killed repair should block the delete at all.