chore(cuda): Upgrade all cuda-related IDE workbences to CUDA 12.6

[andyatmiami]

Description

As part of the 2025a release - we want to bump CUDA to the (latest) 12.6.3 version.

This work builds upon the excellent investigation of @daniellutz to bring the upgrade to fruition.

A couple important points to note:

• Previously RStudio and Jupyter were on different version of CUDA (12.1 and 12.4 respectively). This change standardizes the version to 12.6 across the IDEs
• The .repo and licence file previously stored in cuda subfolders for ubi9 and c9s are identical. To avoid unnecessary duplication - the files are now at the root of the cuda/ directory - and sub-folders have been removed.
• There is some uncertainty on whether or not ENV XLA_FLAGS needs to be defined. For now, for consistency, it is always placed as the last instruction in the cuda-base Docker stage prior to restoring USER + WORKDIR to desired values.

Related-to: https://issues.redhat.com/browse/RHOAIENG-19480

How Has This Been Tested?

⚠️ Testing is currently a work in progress

Merge criteria:

• The commits are squashed in a cohesive manner and have meaningful messages.
• Testing instructions have been added in the PR body (for PRs involving changes that are not immediately obvious).
• The developer has manually tested the changes and verified that the changes work

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