ZTimestamp version 26

• Major change: switch ZTimestamp from second to nanosecond precision
• Add ZTimestamp>>#rounded
• Add ZTimestamp>>#truncated
• ZTimestamp class>>#nowTruncated
• Remove ZTimestampSNTPClient and ZTimestampSNTPClientTests as they are no longer needed

ZTimestamp version 25

• Allow for a broader range of IDs to be used to refer to ZTimezone, in particular all those that exist in zoneinfo
• Add some more comments clarifying how ZTimezone loads & caches info
• Fix an issue where a timezone with just 1 subtimezone and no transitions had a faulty subzone index
• Fix spelling of Mercredi
• Introduce ZTimezone current as default for ZCurrentTimezone and document it better
• Remove all usage and references to the local time zone offset since it is basically useless.
• Remove ZTimestamp's internal use of ClockTimezoneOffset as we are far beyond Pharo 3 now.
• Reorganize package structure (split Core and Tests)
• Set up CI infrastructure using GitHub Actions

ZTimestamp version 24

stable version after move to github (one ahead of MC version 23)