chore(build): support build lua-tiktoken on Windows (#128)

Signed-off-by: Hanchin Hsieh <me@yuchanns.xyz>

lua/tiktoken_lib.lua

@@ -7,6 +7,8 @@ H.get_os_name = function()
     return "linux"
   elseif os_name == "Darwin" then
     return "macOS"
+  elseif os_name == "Windows_NT" then
+    return "windows"
   else
     error("Unsupported operating system: " .. os_name)
   end
@@ -14,7 +16,7 @@ end
 
 H.library_path = function()
   local os_name = H.get_os_name()
-  local ext = os_name == "linux" and "so" or "dylib"
+  local ext = os_name == "linux" and "so" or (os_name == "macOS" and "dylib" or "dll")
   local dirname = string.sub(debug.getinfo(1).source, 2, #"/tiktoken_lib.lua" * -1)
   return dirname .. ("../build/?.%s"):format(ext)
 end