Reaeration field and lab collection

Field and external laboratory data from salt-tracer and gas injection field measurements, including stream widths, inert gas concentrations, conservative tracer concentrations, and conductivity times series. In April, 2025, SF6 releases for this data product were discontinued at all NEON sites, described in more detail in the following [`Data Notification`](https://www.neonscience.org/impact/observatory-blog/discontinuing-sf6-releases-part-reaeration-dp120190001-all-neon-sites). Conservative salt slug experiments to measure stream travel time and calculate mean depth will continue at all sites.