Update `versionmangle` to handle time in filename

Update `versionmangle` to handle time in filename

Since 2024-03-19, the database files have a time component in their
filenames. Previously, versionmange handled the date component,
dropping the dashes from 2024-03-19 to 0~20240319. However, now the
time component gets added as a Debian revision, and messes the logic
up. So with this commit the versionmange transforms timestamp into
a similar upstream component, from -03:45 to ~0345.

Upstream filename 2024-03-20-03:45 now becomes 0~20240320~0345,
while retaining 2024-03-19 as 0~20240319 for backwards compatibility.