This PR Introduces new dnn::ArgKind: DNN_ARG_CACHED. This can be used to store cache of dynamic size, which persists between runs of a net.

The cache management (allocation, growing, writing) is intended to be performed directly from the layers.
The memory is organized in pages, where each page is a Mat.

Caching is particularly useful for LLM inference, where Key and Value tokens are reused for generating subsequent tokens. The KV Caching will be added to attention layer.

Pull Request Readiness Checklist

See details at https://github.com/opencv/opencv/wiki/How_to_contribute#making-a-good-pull-request

• I agree to contribute to the project under Apache 2 License.
• To the best of my knowledge, the proposed patch is not based on a code under GPL or another license that is incompatible with OpenCV
• The PR is proposed to the proper branch
• There is a reference to the original bug report and related work
• There is accuracy test, performance test and test data in opencv_extra repository, if applicable
  Patch to opencv_extra has the same branch name.
• The feature is well documented and sample code can be built with the project CMake

Reference: #27176