Cuvec

- add SWIG support via `cuvec.i` (7)
- add & document `example_swig`
- improve & document `example_mod`
- fix external `include`s
+ multiple definitions
+ missing cuda runtime header
+ use of static & templates
+ namespace clashes
- statically link CUDA libraries
- use macros to reduce code duplication
- add and fix tests
- add performance checks
- misc code tidy

- add `__cuda_array_interface__` (4)
- add tests
- update documentation

- fix `asarray` not copying on `ndarray.view(CuVec)` (2)
- fix potential name clashes with namespaces
- consistent name capitalisation in documentation

- add half-precision (fp16/`float16`/`__half`/`'e'`) (1)
- fix unneeded `asarray` memcopy on raw objects
- fix external `include "cuvec.cuh"`
+ remove unneeded cuhelpers
- update supported `typecodes`
- and external module example
- add performance test
- add `asarray` tests

- add proper `asarray` equivalent
+ add tests
- minor tidy

- fix external allocation (https://github.com/python/cpython/pull/24283)