Safer Handle Initialisation

- made `llama_backend_init` private. This is automatically called, there is no way it can correctly be used externally.
 - made `llama_token_to_piece` safe (Span instead of pointer)

- Wrapped some native functions which take (pointer, length) in function which take a `span` instead.

- Made `NativeApi` into a `static class` (it's not intended to be instantiated)
 - Moved `LLamaTokenType` enum out into a separate file
 - Made `LLamaSeqId` and `LLamaPos` into `record struct`, convenient to have equality etc

bump sk to 1.0.1 & km to 0.18

Improved support for AVX512

- Enabled more features in build process (VBMI and VNNI)
 - Added runtime checking for this features
 - Improved runtime checking to no longer require dotnet8.0

Context Set Seed

Renamed `llama_sample_temperature` to `llama_sample_temp`

- Renamed `LLamaModelKvOverride` to `LLamaModelMetadataOverride`

- build run: https://github.com/SciSharp/LLamaSharp/actions/runs/7196891440
 - commit: 9fb13f9584

Custom Sampling Pipelines

- Added BaseSamplingPipeline which provides a base impl of `ISamplingPipeline`
 - Added `DefaultSamplingPipeline` which mimics normal llama.cpp sampling

- Added an example usage to one of the tests

- Added a `Sample` method to `LLamaContext` which uses a custom pipeline
 - Modified all executors to use the custom pipeline if it exists

- Saves with serialized ChatHistory of session
- Only allows use of ChatHistory.Message (instead of raw text)
   for easy post-processing with IHistoryTransform implementation
- Provides History Management methods
- Allows user to regenerate last assistant message