Panic with --mtime/--atime/--ctime on DST change days #641

When local midnight is ambiguous or skipped because of a DST change,
dust panics if any of the time filters is used.

Repro (Egypt moved clocks back at 24:00 on 2025-10-30):

TZ=Africa/Cairo faketime '2025-10-31 12:00' dust --mtime 0 .

thread 'main' panicked at src/config.rs:218:10:
Ambiguous local time, ranging from 2025-10-31T00:00:00+02:00
to 2025-10-31T00:00:00+03:00

The cause is the .unwrap() on Local.from_local_datetime() in
get_current_date_epoch_seconds().

On the spring-forward day (2025-04-25) midnight does not exist at all,
and test_get_current_date_epoch_seconds fails there too.