Enforce a file extension for files saved by the MCP server

[OrKoN]

By ensuring that file extensions are set on files written by the MCP server, it makes it less likely that other types of files are overwritten by the MCP server. To be used on conjunction with #1860

[andrewpsp]

In the context of explicitly vs implicitly it would make since to establish a prefix or suffix; a grouping signature that will denote a resource of Devtools written by the MCP. For example how most image generation outputs are exquisitely detailed in the filename, the extension becomes not as important. For Devtool's case the MCP may write various types of files in which opaqueness would be optimal.