- Minor changes to cleanup some of the compiler warnings

Type conversion is now done in the property rather than the utils class and uses the System.Convert class to ensure consistency.

- Deleted `NativeInfo` (internal class, not used anywhere)

- Converted `SafeLLamaContextHandle` to take a `ReadOnlySpan` for Eval, narrower type better represents what's really needed

Multi Context

* Added a bool to sbyte Utils convertor

As an attempt to avoid using any MarshalAs attribute for .Net Framework support this Utils method will take in a bool value and return a 1 for true or 0 for false sbyte.

* Changed all bool "MarshalAs" types to sbytes

Changed all previous BOOL types with "MarshalAs" attributes to SBYTEs and changed all the setters of them to use the Utils.BoolToSignedByte() convertor method.

* Fixed Utils bool convertor & added sbyte to bool

Improved the Utils bool convertor just casting an sbyte value to get rid of the unneeded sbyte array and added an sbyte to bool convertor to convert back the way to a C# bool assuming any positive value above 0 is a bool and no bools are packed in the single byte integer.

* bool to & from sbyte conversions via properties

All 1byte bools are now handled where they "sit", via public properties which perform the conversions to keep all external data able to communicate as it did before.

- Sanity checking that weights are not disposed when creating a context from them
 - Further simplified `Utils.InitLLamaContextFromModelParams`

The biggest single change is renaming `LLamaModel` to `LLamaContext`

- Added disposal check into `SafeLLamaContextHandle`

- Also refactored it to return an `int[]` instead of an `IEnumerable<int>`, solving the "multiple enumeration" problems at the source!

It solves the problem with netstandard2 (is it really netstandard2 a thing right now?)
Change context to solve problems.

5f631c2679

This change _only_ implements the low level API and makes no effort to update the LlamaSharp higher level abstraction.

It is built upon llama `b3f138d`, necessary DLLs are **not** included in this commit.