Fix dasdae format reads with datetime-like coords

Description

This PR fixes an issue which caused DASCore to fail to read DASDAE formatted patches if an attached coordinate was associated with a dimension and a datetime-type.

It also fixed an issue that would cause selecting with multiple coordinates that reference to the same dimension to not perform the selection properly (only the second selection was performed previously).

Checklist

I have (if applicable):

[ ] referenced the GitHub issue this PR closes.
[ ] documented the new feature with docstrings or appropriate doc page.
[ ] included a test. See testing guidelines.
[ ] your name has been added to the contributors page (docs/contributors.md).
[ ] added the "ready_for_review" tag once the PR is ready to be reviewed.

Codecov Report

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

Project coverage is 99.53%. Comparing base (f93ac93) to head (c23d4e5).

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #355 +/- ## ======================================= Coverage 99.53% 99.53% ======================================= Files 94 94 Lines 7341 7366 +25 ======================================= + Hits 7307 7332 +25 Misses 34 34 ``` | [Flag](https://app.codecov.io/gh/DASDAE/dascore/pull/355/flags?src=pr&el=flags&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=DASDAE) | Coverage Δ | | |---|---|---| | [unittests](https://app.codecov.io/gh/DASDAE/dascore/pull/355/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=DASDAE) | `99.53% <100.00%> (+<0.01%)` | :arrow_up: | Flags with carried forward coverage won't be shown. [Click here](https://docs.codecov.io/docs/carryforward-flags?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=DASDAE#carryforward-flags-in-the-pull-request-comment) to find out more.

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DASDAE / dascore