[CUCO][FEA]: Migrate host and device `find` APIs for fixed_capacity_map

[PointKernel]

Is this a duplicate?

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Area

CUDA Experimental (cudax)

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

Follow up of #7705, the PR migrates insert and contains APIs to cudax and I'd like to do the same for find.

Describe the solution you'd like

Migrate the host and device find APIs and add corresponding tests and benchmarks to ensure the migration introduces no performance regressions.

Describe alternatives you've considered

No response

Additional context

No response