Remove dependency of backend CPU and fix CI

See merge request eclipse/aidge/aidge_backend_opencv!9

Change tensorimpl opencv `future_std::span<cv::Mat>` to `cv::Mat`

See merge request eclipse/aidge/aidge_backend_opencv!4

[Upd] Code rework

See merge request !7

Update TensorImpl constructor to take the tensor  dimensions instead of the number of elements and override resize function.

Add CI for backend opencv

See merge request eclipse/aidge/aidge_backend_opencv!6

- [Optimize] add const, inline, noexcept where possible
- [Utils] add DataUtils file for conversion from cv type to cpp type
- [Syntax] Stimulis -> Stimuli and Stimuli -> Stimulus
- [#define] Use standard Aidge syntax format
- [Licence] add where missing
- [#include] add what is used and remove what is not
- [class] uniformize class member definition order
- [types] change size_t for std::size_t from <stddef> for uniformazation
- [types] change integer types for exact-width integers from <cstddint>
- Remove end-of-line spaces