fix[cartesian]: Protect K write against dynamic access

[FlorianDeconinck]

Description

We allowed offset-writes in K in a previous PR e.g.

out_field[0, 0, 1] = value

but we let open the possibility for the offset to be a dynamic value which would escape any extent analysis. E.g.

index = value ** 29382938
out_field[0, 0, index] = other_value

The time might come where a legit case shows up and we could imagine introducing a mitigating strategy. Until that fateful day, we restrict access to literals.

Requirements

• All fixes and/or new features come with corresponding tests.
• Important design decisions have been documented in the approriate ADR inside the docs/development/ADRs/ folder.

If this PR contains code authored by new contributors please make sure:

• The PR contains an updated version of the AUTHORS.md file adding the names of all the new contributors.

[FlorianDeconinck]

Won't do as we actually have the case listed above.

We logged a mitigation task which seems to us the best way to meet feature need and performance #1684