Candidate Measurement Fix, main branch (2026.05.13.)

[krasznaa]

I noticed this one in #1259. Once again this is an issue that CUDA only complains about when paired with Clang as the host compiler. Namely that:

[build] /home/krasznaa/ATLAS/projects/traccc/traccc/core/include/traccc/fitting/kalman_filter/measurement_selector.hpp(31): error #20012-D: __host__ annotation is ignored on a function("operator<=>") that is explicitly defaulted on its first declaration
[build]       __attribute__((host)) __attribute__((device))
[build]                      ^
[build] 
[build] Remark: The warnings can be suppressed with "-diag-suppress <warning-number>"
[build] 
[build] /home/krasznaa/ATLAS/projects/traccc/traccc/core/include/traccc/fitting/kalman_filter/measurement_selector.hpp(31): error #20012-D: __device__ annotation is ignored on a function("operator<=>") that is explicitly defaulted on its first declaration
[build]       __attribute__((host)) __attribute__((device))
[build]                                            ^

I've run into similar things in vecmem a couple of times in the past. That one cannot use __device__ and __host__ declarations for auto-generated functions. Luckily since the function is anyway declared to be constexpr, nvcc uses it happily even without the __device__ declaration.

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

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