FixedSizeQueue:
 - Enqueue would always stop one short of filling the capacity
 - Fill would only _replace_ existing items. It was only used in a place where there were not existing items! Removed the method entirely.

LLamaGrammarElement:
 - Converted into a `record` struct, removed all of the (now unnecessary) equality stuff.

* Added the low level bindings to beam search.

Add GGUF support

- Made all the mechanics of grammar parsing (GBNFGrammarParser, ParseState) internal. Just call `Grammar.Parse("whatever")`.
 - Added a `GrammarRule` class which validates elements on construction (this allows constructing grammar without parsing GBNF).
   - It should be impossible for a `GrammarRule` to represent an invalid rule.

- Equality, hashing etc all implemented automatically
 - Default values are defined in just one place (the properties) instead of the constructor as well
 - Added test to ensure that serialization works properly

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

- Integrated grammar into sampling
 - Added a test for the grammar sampling