Remove conversion of Matplotlib artifacts to Plotly objects for storage

When a Matplotlib figure is stored as an artifact to the Simvue server, it is converted to a Plotly artifact and stored that way (I assume so that it can be viewed within the UI, which is very useful!). However when it is pulled back from the server using the client, the figure is returned as a Plotly object, instead of the Matplotlib figure originally stored. Can the figure be converted back to Matplotlib before being returned, so that the user gets back the same artifact which they stored?

从检索已存储 artifact 的客户端路径开始，跟踪 Matplotlib 图形的序列化和重建过程。检查 issue 中描述的现有 Matplotlib 到 Plotly 处理，并添加有针对性的往返测试。完成的标准是：存储在 Simvue 上的 Matplotlib 图形能够以 Matplotlib 图形的形式返回，同时现有 Plotly artifact 的检索仍然正常工作。