Avoid heap allocation with native strings whenever possible

[BeanCheeseBurrito]

In the current API, strings that need to be passed over to the native side are always allocated on the heap with Marshal.StringToHGlobalAnsi using the NativeString helper struct.

Example:

{
    string managedString = "Hello World";
    using NativeString nativeString = (NativeString)managedString; // Heap allocation
    random_function(nativeString); // NativeStrings are implicitly casted to byte*/sbyte*
    // String is freed at the end of the scope
}

Heap allocations are unnecessary in places where strings are freed immediately after use and should be rewritten to use stack allocated memory instead.

Example:

{
    string managedString = "Hello World";
    byte* nativeString = stackalloc byte[managedString.Length + 1];
    StackAllocString(nativeString, managedString);
    random_function(nativeString);
}