src: Use shorter inline variables for detail type traits

[stotko]

While the use of type traits from the C++ standard library have been simplified in #333, our own implementation-specific traits are still referenced by the classic *::value notation. Port these traits to the newer *_v versions as well for consistency and better readability.

Partially addresses #314

[codecov[bot]]

Codecov Report

Base: 97.14% // Head: 97.14% // No change to project coverage :thumbsup:

Coverage data is based on head (0ec3ad2) compared to base (aecccfd). Patch coverage: 100.00% of modified lines in pull request are covered.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #335 +/- ## ======================================= Coverage 97.14% 97.14% ======================================= Files 32 32 Lines 2346 2346 ======================================= Hits 2279 2279 Misses 67 67 ``` | [Impacted Files](https://codecov.io/gh/stotko/stdgpu/pull/335?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/unordered\_base.cuh](https://codecov.io/gh/stotko/stdgpu/pull/335/diff?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Patrick+Stotko#diff-c3JjL3N0ZGdwdS9pbXBsL3Vub3JkZXJlZF9iYXNlLmN1aA==) | `100.00% <ø> (ø)` | | | [src/stdgpu/impl/unordered\_base\_detail.cuh](https://codecov.io/gh/stotko/stdgpu/pull/335/diff?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Patrick+Stotko#diff-c3JjL3N0ZGdwdS9pbXBsL3Vub3JkZXJlZF9iYXNlX2RldGFpbC5jdWg=) | `96.00% <ø> (ø)` | | | [src/stdgpu/impl/unordered\_map\_detail.cuh](https://codecov.io/gh/stotko/stdgpu/pull/335/diff?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Patrick+Stotko#diff-c3JjL3N0ZGdwdS9pbXBsL3Vub3JkZXJlZF9tYXBfZGV0YWlsLmN1aA==) | `100.00% <ø> (ø)` | | | [src/stdgpu/impl/unordered\_set\_detail.cuh](https://codecov.io/gh/stotko/stdgpu/pull/335/diff?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Patrick+Stotko#diff-c3JjL3N0ZGdwdS9pbXBsL3Vub3JkZXJlZF9zZXRfZGV0YWlsLmN1aA==) | `100.00% <ø> (ø)` | | | [src/stdgpu/impl/vector\_detail.cuh](https://codecov.io/gh/stotko/stdgpu/pull/335/diff?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Patrick+Stotko#diff-c3JjL3N0ZGdwdS9pbXBsL3ZlY3Rvcl9kZXRhaWwuY3Vo) | `94.00% <ø> (ø)` | | | [src/stdgpu/unordered\_map.cuh](https://codecov.io/gh/stotko/stdgpu/pull/335/diff?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Patrick+Stotko#diff-c3JjL3N0ZGdwdS91bm9yZGVyZWRfbWFwLmN1aA==) | `100.00% <ø> (ø)` | | | [src/stdgpu/unordered\_set.cuh](https://codecov.io/gh/stotko/stdgpu/pull/335/diff?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Patrick+Stotko#diff-c3JjL3N0ZGdwdS91bm9yZGVyZWRfc2V0LmN1aA==) | `100.00% <ø> (ø)` | | | [src/stdgpu/vector.cuh](https://codecov.io/gh/stotko/stdgpu/pull/335/diff?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Patrick+Stotko#diff-c3JjL3N0ZGdwdS92ZWN0b3IuY3Vo) | `100.00% <ø> (ø)` | | | [src/stdgpu/impl/memory\_detail.h](https://codecov.io/gh/stotko/stdgpu/pull/335/diff?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Patrick+Stotko#diff-c3JjL3N0ZGdwdS9pbXBsL21lbW9yeV9kZXRhaWwuaA==) | `99.03% <100.00%> (ø)` | | Help us with your feedback. Take ten seconds to tell us [how you rate us](https://about.codecov.io/nps?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Patrick+Stotko). Have a feature suggestion? [Share it here.](https://app.codecov.io/gh/feedback/?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Patrick+Stotko)

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