Incorporate timestamp when using an "as_of" date to get the VersionID of an S3 object

[bsweger]

This is a follow up to #23

That PR added the ability to look up an S3 versionID for a specific date, but as noted in that PR review, we really should make that feature "timestamp aware."

Definition of Done

• If no as_of date is supplied when downloading files from Nextstrain's S3 bucket, the default date should be UTC datetime.now() (i.e., current timestamp) instead of the current date at midnight.
• Allow user to specify a timestamp in addition to a date. If user specifies an as_of date without a timestamp, default the time to midnight UTC.

2025-01-3 update: If someone passes YYYY-MM-DD in string format (i.e., 2025-01-01), Cladetime should interpret that as datetime(2024, 1, 1, 11, 59, 59). However, if someone passes a Python datetime object without a time (i.e., datetime(2025, 1, 1, 0, 0, 0)), it's hard to interpret intent--maybe they want to use midnight as a time stamp? Therefore, in the latter case, Cladetime should not override the timestamp to 11:59:59)

[bsweger]

@elray1 Am reviewing some old tickets, and I'm not sure I stated the first "definition of done" item correctly.

Cladetime now works exclusively in UTC time, but it sounds like if someone specifies a date w/o a time, the most helpful behavior would be to use 23:59 UTC as the timestamp instead of midnight.

Current behavior:

from cladetime import CladeTime
ct = CladeTime(tree_as_of="2024-09-03")
ct
CladeTime(sequence_as_of=2024-11-13 21:10:23+00:00, tree_as_of=2024-09-03 00:00:00+00:00)

1. Can you confirm that what you want here is tree_as_of set to 2024-09-03 23:59:59+00:00?
2. For unspecified dates (like sequence_as_of, above), ok to leave the default as the current UTC timestamp?

[elray1]

1. Yes, I think setting to the end of the specified date (UTC) is a good choice when a time is not specified.
2. Yes, using the current UTC timestamp is reasonable if nothing is specified.