Add default initialisation to MEMBER_LBOUNDS in FIELD_STACK

[wertysas]

This PR adds default initialisation of the MEMBER_LBOUNDS that is used to define the LBOUNDS of the stack members, ensuring they are always set to 1 if no MEMBER_LBOUNDS argument is passed when creating the map.

This is a small "bugfix-PR" and the only additions are the default initilisation lines in the field stack wrapper and owner FIELD_NEW methods and the field stack tests have been updated to cover this default behaviour.

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By opening this pull request, I affirm the following:

• All authors agree to the Contributor License Agreement.
• The code follows the project's coding standards.
• I have performed self-review and added comments where needed.
• I have added or updated tests to verify that my changes are effective and functional.
• I have run all existing tests and confirmed they pass.

[awnawab]

Thanks a lot @wertysas for finding this subtle bug 🙏 As discussed offline, the gpu test was redundant since this is a field initialisation bug, and is independent of the offload status.