[Feature] Support compiling the grammar JIT.

[Seven-Streams]

This PR enables the xgrammar to compile the grammar just in time. To determine whether a grammar should be compiled just in time, you can use the code as follows:

grammar = xgr.Grammar.builtin_json_grammar() 
tokenizer = AutoTokenizer.from_pretrained("meta-llama/Llama-2-7b-chat-hf")
compiler = xgr.GrammarCompiler(xgr.TokenizerInfo.from_huggingface(tokenizer), is_jit=True)
compiled_grammar = compiler.compile_grammar(grammar)
... # the same codes with the pre-computed compiled_grammar.

Signed-off-by: Yuchuan [email protected]