Update spack.yaml for UM with init compile flags

[Whyborn]

Added variable initialisation compile flags to the UM to test non-determinism hypothesis.

This branch is not intended to be merged. Testing hypothesis of garbage memory being written as cause of non-determinism by setting scalars and arrays to have value 0 on initialisation.

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🚀 The latest prerelease access-esm1p6/pr63-1 at 8d2c6da is here: #63 (comment) 🚀

[github-actions]

🚀 Attempted to deploy access-esm1p6 Prerelease pr63-1 with commit 8d2c6da

🖥️ Gadi Deployment ✔️

Usage Instructions

This access-esm1.6 model will be deployed to Gadi as:

• dev_2025.03.1 as a Release (when merged).
• pr63-1 as a Prerelease (during this PR).

This Prerelease is accessible on Gadi using:

module use /g/data/vk83/prerelease/modules
module load access-esm1p6/pr63-1

When using the above modules, the binaries shall be on your $PATH.

For advanced users, this Prerelease is also accessible on Gadi via /g/data/vk83/prerelease/apps/spack/0.22/spack in the access-esm1p6-pr63-1 environment.

Configuration Information

This Prerelease is deployed using:

• access-nri/spack on branch 0.22
• access-nri/spack-packages version 2025.03.002
• access-nri/spack-config version 2025.02.2

If the above was not what was expected, commit changes to config/versions.json in this PR.

[Whyborn]

Adding variable initialisation flags did affect the results, confirming the hypothesis.