🍒 chore(cloudxr): bump runtime SDK version to 6.3.0-rc3

[nv-mhaselton]

Description

Backport 0ec416b95 into release/1.4.x.

On main, this followed #873, which landed CloudXR Runtime SDK 6.3.0-rc2. The 1.4 branch currently pins 6.2.1, so this advances it directly to 6.3.0-rc3.

RC3 is the newest runtime published on NGC and, unlike earlier versions, provides the experimental archives required by the cloudxr_exp wheel bundle.

The SDK is consumed as prebuilt shared objects. CMake extracts the archive and removes include/ and plugins/, so this change only updates the runtime version pin.

Type of change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Documentation update

Testing

• Ran SKIP=check-copyright-year pre-commit run --all-files.
• Built an x86_64 CPython 3.12 wheel locally with ENABLE_CLOUDXR_EXP_BUNDLE=ON.
• Verified the wheel by launching camera_viz in XR mode with the bundled RC3 runtime.
• The post-merge release/1.4.x CI run will validate private-NGC download and wheel packaging. Fork PR workflows cannot access the required NGC secret.

Checklist

• I have read and understood the contribution guidelines
• I have run the linter and formatter with SKIP=check-copyright-year pre-commit run --all-files
• Documentation changes are not required for this version-pin backport
• Testing is described above
• I have signed off all my commits (git commit -s) per the DCO

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[nv-mhaselton]

Replaced #894