fix 359

[d-chambers]

Description

This PR fixes #359 by adding a pandas.Series dispatch to dascore.utils.time.to_float.

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]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 99.54%. Comparing base (5aad001) to head (77f60d3).

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #377   +/-   ##
=======================================
  Coverage   99.54%   99.54%           
=======================================
  Files          97       97           
  Lines        7622     7626    +4     
=======================================
+ Hits         7587     7591    +4     
  Misses         35       35           

Flag	Coverage Δ
unittests	99.54% <100.00%> (+<0.01%)	⬆️

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