[FEA]: Add CI check for unqualified uses of cuda:: namespace

[jrhemstad]

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Area

General CCCL

Is your feature request related to a problem? Please describe.

Inspired by #1705, we should always fully qualify uses of the cuda:: namespace as ::cuda::.

Describe the solution you'd like

Add a CI check that greps for unqualified uses of cuda:: namespace.

This check should ignore tests and samples.

Describe alternatives you've considered

No response

Additional context

No response