Explicit Series Close Call

[ax3l]

In some interactive workflows (e.g., Jupyter), people want to generate a file - plot it - regenerate it - plot again.

If we keep the read file open in openPMD-viewer, then a user cannot overwrite it.

We could add an explicit close call, that closes the file handles (similar to openPMD-api).
For user-friendliness, subsequent open calls should reopen the files needed (even if it adds latency if done accidentally).

Example workflow: LASY-org/lasy#187