Adding Literal Enum support.

[nova-land]

Adding Enum support with the following format:

enum EnumName { ChoiceA, ChoiceB, ChoiceC }

So we can have the following interface:

enum Tool { WebSearch, Wikipedia, Calculator, FileRead, FileWrite }

interface ReAct {
  select: Tool;
  reason: string;
}

With the following output

root ::= ReAct
ReAct ::= "{"   ws   "\"select\":"   ws   enumTool   ","   ws   "\"reason\":"   ws   string   "}"
ReActlist ::= "[]" | "["   ws   ReAct   (","   ws   ReAct)*   "]"
string ::= "\""   ([^"]*)   "\""
boolean ::= "true" | "false"
ws ::= [ \t\n]*
number ::= [0-9]+   "."?   [0-9]*
stringlist ::= "["   ws   "]" | "["   ws   string   (","   ws   string)*   ws   "]"
numberlist ::= "["   ws   "]" | "["   ws   string   (","   ws   number)*   ws   "]"
enumTool ::= "\"" "WebSearch" "\"" | "\"" "Wikipedia" "\"" | "\"" "Calculator" "\"" | "\"" "FileRead" "\"" | "\"" "FileWrite" "\""

The additional code provides the default Grammar Register with original grammar elements and then adds dynamic Enum Grammar Elements based on the source file.

Also, separate some helper functions into util.py.

[a10y]

Thank you! Really appreciate you putting in the effort here to clean things up and add tests as well!

I have a few small tweaks but I'll make them after merge :)