Feature: User-friendly time parsing

[atimin]

Current problem

When using the 'reduct cp' command to copy data for a certain time interval, users must specify the time in full ISO format.

reduct-cli cp server-1/data server-2/data --start  2026-01-01T00:00:00+00:00

It's too verbose and error prone.

Possible solution

Users should be able to specify times in shorter formats:

Only date (local time): `2026-01-01`
Local time without time zone: `2026-01-01T20:00:00`
From now: ` now - 1{s|m|h|d|y}`

Additional context

No response

Code of Conduct

• I agree to follow this project's Code of Conduct