execution: Apply is_execution_policy to overload more algorithms conditionally

[stotko]

While #377 improved the overload resolution situation with the containers, the same issue also applies to the free functions defined in algorithm, memory, and numeric. Conditionally enable the involved functions like in the case of the containers to closer adhere to the C++ standard.

[codecov[bot]]

Codecov Report

Patch and project coverage have no change.

Comparison is base (53c1f9f) 97.36% compared to head (c7c6328) 97.36%.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #378 +/- ## ======================================= Coverage 97.36% 97.36% ======================================= Files 31 31 Lines 2547 2547 ======================================= Hits 2480 2480 Misses 67 67 ``` | [Impacted Files](https://app.codecov.io/gh/stotko/stdgpu/pull/378?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Patrick+Stotko) | Coverage Δ | | |---|---|---| | [src/stdgpu/impl/algorithm\_detail.h](https://app.codecov.io/gh/stotko/stdgpu/pull/378?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Patrick+Stotko#diff-c3JjL3N0ZGdwdS9pbXBsL2FsZ29yaXRobV9kZXRhaWwuaA==) | `100.00% <ø> (ø)` | | | [src/stdgpu/impl/memory\_detail.h](https://app.codecov.io/gh/stotko/stdgpu/pull/378?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Patrick+Stotko#diff-c3JjL3N0ZGdwdS9pbXBsL21lbW9yeV9kZXRhaWwuaA==) | `99.00% <ø> (ø)` | | | [src/stdgpu/impl/numeric\_detail.h](https://app.codecov.io/gh/stotko/stdgpu/pull/378?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Patrick+Stotko#diff-c3JjL3N0ZGdwdS9pbXBsL251bWVyaWNfZGV0YWlsLmg=) | `100.00% <ø> (ø)` | |

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