Drop the spectroscopic_selection in rail_base and host it in rail_astro_tools

[ztq1996]

Problem & Solution Description (including issue #)

We are bringing the spectroscopic selection to rail_astro_tools, and dropping the one in rail_base. Here I am bringing the up-to-date version in rail_base to rail_astro_tools. The differences are made by @OliviaLynn, and are all reviewed in rail_base, so this should be straightforward.

Code Quality

• [ ] My code follows the code style of this project
• [ ] I have written unit tests or justified all instances of #pragma: no cover; in the case of a bugfix, a new test that breaks as a result of the bug has been added
• [ ] My code contains relevant comments and necessary documentation for future maintainers; the change is reflected in applicable demos/tutorials (with output cleared!) and added/updated docstrings use the NumPy docstring format
• [ ] Any breaking changes, described above, are accompanied by backwards compatibility and deprecation warnings

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 96.78%. Comparing base (8c2733e) to head (dbc4911).

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #95 +/- ## ========================================== - Coverage 97.11% 96.78% -0.34% ========================================== Files 32 31 -1 Lines 1770 1585 -185 ========================================== - Hits 1719 1534 -185 Misses 51 51 ```

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