fix(encode_number): support up to 20 significant digits when encoding decmials, return string value of integers

As mentioned in rxi#42 (comment) - Lua 5.3+ supports 64 bit integers. This change modifies the string encoding of numbers to align with those changes.

Author: dtfiedler

json.lua

@@ -108,7 +108,12 @@ local function encode_number(val)
   if val ~= val or val <= -math.huge or val >= math.huge then
     error("unexpected number value '" .. tostring(val) .. "'")
   end
-  return string.format("%.14g", val)
+  -- Handle integer values separately to avoid floating-point conversion
+  if math.type(val) == "integer" then
+    return string.format("%d", val) -- Format as an integer
+  else
+  -- Use 20 significant digits for non-integer numbers
+	return string.format("%.20g", val)
 end