added formating functions

tests/format.sl

@@ -0,0 +1,68 @@
+import stdlib/stdlib.sl
+import stdlib/io.sl
+
+word main
+    # --- indexof ---
+    "hello" 108 indexof puti cr             # 'l' at index 2
+    "hello" 122 indexof puti cr             # 'z' not found -> -1
+
+    # --- count_char_in_str ---
+    "hello world" 108 count_char_in_str     # 3 l's
+    puti cr 2drop
+
+    # --- format1s (single string substitution) ---
+    "world" "hello %" format1s
+    2dup puts free
+
+    # --- format1i (single int substitution) ---
+    42 "the answer is %" format1i
+    2dup puts free
+
+    # --- formats (multi string substitution) ---
+    "Bob" "Alice" "% and %" formats
+    2dup puts free
+
+    # --- formati (multi int substitution) ---
+    2 1 "a: %, b: %" formati
+    2dup puts free
+
+    # --- edge: no '%' ---
+    "no placeholders" formati
+    puts
+
+    # --- edge: '%' at start ---
+    "X" "% is first" format1s
+    2dup puts free
+
+    # --- edge: '%' at end ---
+    "Y" "last is %" format1s
+    2dup puts free
+
+    # --- format (mixed %i and %s) ---
+    "hello" 1 "a: %i, b: %s" format
+    2dup puts free
+
+    # --- format: single %i ---
+    42 "answer is %i" format
+    2dup puts free
+
+    # --- format: single %s ---
+    "world" "hello %s" format
+    2dup puts free
+
+    # --- format: three mixed ---
+    "bar" 123 "foo" "%s: %i and %s" format
+    2dup puts free
+
+    # --- format: no placeholders ---
+    "nothing here" format
+    puts
+
+    # --- format: %s at start and end ---
+    "B" "A" "%s and %s" format
+    2dup puts free
+
+    # --- format: %i at boundaries ---
+    2 1 "%i+%i" format
+    2dup puts free
+end