Automatically add the absorption edge to metadata

This should be easier with qxscan, but may be also doable with a regular energy scan. Use [`xraydb`](https://github.com/xraypy/XrayDB).

Start by locating the qxscan and regular energy-scan entry points that populate scan metadata, then review how xraydb provides absorption-edge information. Done means the appropriate absorption edge is automatically added to metadata for the supported scan path, with the behavior verified by the project’s existing checks.

Written by the indexing model from the issue text.