Add detailed logging for image conversions on cache miss

Log includes:
- file path
- input/output format
- input/output size in bytes
- input/output dimensions
- size ratio (percentage)

Also adds InputWidth, InputHeight, InputFormat to ProcessResult

internal/imgcache/processor.go

@@ -93,6 +93,9 @@ func (p *ImageProcessor) Process(
 		ContentType:   ImageFormatToMIME(outputFormat),
 		Width:         finalBounds.Dx(),
 		Height:        finalBounds.Dy(),
+		InputWidth:    origWidth,
+		InputHeight:   origHeight,
+		InputFormat:   format,
 	}, nil
 }