GH-125: Allow null timestamp holder sans timezone

[Kaustav-Sarkar]

Description

Fixes an IllegalArgumentException in TimeStamp*TZVector.set/setSafe when unsetting values using a holder with a null timezone. The validation logic now correctly ignores the timezone check when holder.isSet <= 0, allowing default-constructed holders to be used for unsetting values as expected.

Comprehensive tests added for all timestamp precisions (Micro, Milli, Nano, Sec) to verify the fix and ensure the existing workaround (setting explicit timezone) remains supported.

Closes #125 .

[Kaustav-Sarkar]

Please set labels, I do not have permission

[lidavidm]

I think it'd be more natural to move the else block below as the second conditional check, so we aren't repeating boolean clauses.

[jbonofre]

I agree, it looks more "logical".

[jbonofre]

This looks better to me.

[Kaustav-Sarkar]

Could not find a package configuration file provided by "lz4" with any of
    the following names:
  
      lz4Config.cmake
      lz4-config.cmake
  
    Add the installation prefix of "lz4" to CMAKE_PREFIX_PATH or set "lz4_DIR"
    to a directory containing one of the above files.  If "lz4" provides a
    separate development package or SDK, be sure it has been installed.

The build fails with this issue, I do not see how it is related to my changes. Do I need to add anything else to get this PR merged?