2510 hi goodtimes Add xarray accessor for handling goodtimes (IMAP-Science-Operations-Center#2529)

* Add hi_goodtimes with Goodtimes class to be used for storing goodtimes data through processing and writing goodtimes text file

* Convert Goodtimes class to dataset accessor methods

* Apply suggestions from code review

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

* Respond to copilot PR comments

* PR feedback

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Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

Author: tmplummer