Introduce Value_Type.Null, fix edge cases for read_many

[radeusgd]

Pull Request Description

• Closes Introduce a Value_Type.Null. #6281

Important Notes

Checklist

Please ensure that the following checklist has been satisfied before submitting the PR:

• The documentation has been updated, if necessary.
• Screenshots/screencasts have been attached, if there are any visual changes. For interactive or animated visual changes, a screencast is preferred.
• All code follows the
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  TypeScript,
  and
  Rust
  style guides. In case you are using a language not listed above, follow the Rust style guide.
• Unit tests have been written where possible.
• If meaningful changes were made to logic or tests affecting Enso Cloud integration in the libraries,
  or the Snowflake database integration, a run of the Extra Tests has been scheduled.
  • If applicable, it is suggested to paste a link to a successful run of the Extra Tests.

[radeusgd]

Changes affect Snowflake so I'm running the Extra suite:

• https://github.com/enso-org/enso/actions/runs/12145121839

I expect it to fail because it is failing on develop. Yet I want to see if there are no more failures than what is expected.

GitHub

Extra Nightly Tests · enso-org/enso@edfeb06

Enso Analytics is a self-service data prep and analysis platform designed for data teams. - Extra Nightly Tests · edfeb06

[radeusgd]

Followup to fix Nothing * Nothing: #11751