YJIT: refactor format_number (#8869)

Replace enumerators with simpler and faster version that only inserts commas before '.' or end of integer string.

yjit.rb

@@ -437,11 +437,10 @@ module RubyVM::YJIT
 
     # Format large numbers with comma separators for readability
     def format_number(pad, number)
-      integer, decimal = number.to_s.split(".")
-      d_groups = integer.chars.reverse.each_slice(3)
-      with_commas = d_groups.map(&:join).join(',').reverse
-      formatted = [with_commas, decimal].compact.join(".")
-      formatted.rjust(pad, ' ')
+      s = number.to_s
+      i = s.index('.') || s.size
+      s.insert(i -= 3, ',') while i > 3
+      s.rjust(pad, ' ')
     end
 
     # Format a number along with a percentage over a total value