Use array tuple keys for style_func map

Replace string keys like "0,1" with [0, 1] array tuples in the
style_func precomputed map. Avoids string allocation per lookup
and is more idiomatic Ruby.

Author: khasinski

lib/lipgloss/table.rb

@@ -69,14 +69,14 @@ def style_func(rows:, columns:, &block)
       # Header row
       columns.times do |column|
         style = block.call(HEADER_ROW, column)
-        style_map["#{HEADER_ROW},#{column}"] = style if style
+        style_map[[HEADER_ROW, column]] = style if style
       end
 
       # Data rows
       rows.times do |row_idx|
         columns.times do |column|
           style = block.call(row_idx, column)
-          style_map["#{row_idx},#{column}"] = style if style
+          style_map[[row_idx, column]] = style if style
         end
       end
 
@@ -210,7 +210,7 @@ def build_data_row(row_data, col_widths, chars, row_idx)
 
         # Apply style_func if available
         if @style_map
-          style = @style_map["#{row_idx},#{i}"]
+          style = @style_map[[row_idx, i]]
           cell_text = style.render(cell_text) if style
         end