strconv: fix format.md example snippets (#12642)

vlib/strconv/format.md

@@ -93,7 +93,9 @@ The Type field can be any of:
 
 various types
 
-```v oksyntax
+```v
+import strconv
+
 a0 := u32(10)
 b0 := 200
 c0 := byte(12)
@@ -102,7 +104,7 @@ ch0 := `B`
 f0 := 0.312345
 f1 := 200000.0
 sc0 := 'ciao: [%-08u] %d %hhd [%8s] [%08X] [%-20.4f] [%-20.4f] [%c]'
-temp_s = strconv.v_sprintf(sc0, a0, b0, c0, s0, b0, f0, f1, ch0)
+temp_s := strconv.v_sprintf(sc0, a0, b0, c0, s0, b0, f0, f1, ch0)
 println(temp_s)
 ```
 
@@ -112,13 +114,15 @@ ciao: [10      ] 200 12 [    ciAo] [000000C8] [0.3123              ] [200000.000
 
 integer
 
-```v oksyntax
+```v
+import strconv
+
 a := byte(12)
 b := i16(13)
 c := 14
 d := i64(15)
 sc1 := '==>%hhd %hd %d %ld'
-temp_s = strconv.v_sprintf(sc1, a, b, c, d)
+temp_s := strconv.v_sprintf(sc1, a, b, c, d)
 println(temp_s)
 ```
 
@@ -128,13 +132,15 @@ println(temp_s)
 
 unsigned integer
 
-```v oksyntax
+```v
+import strconv
+
 a1 := byte(0xff)
 b1 := u16(0xffff)
 c1 := u32(0xffffffff)
 d1 := u64(-1)
 sc2 := '%hhu %hu %u %lu'
-temp_s = strconv.v_sprintf(sc2, a1, b1, c1, d1)
+temp_s := strconv.v_sprintf(sc2, a1, b1, c1, d1)
 println(temp_s)
 ```
 
@@ -144,13 +150,15 @@ println(temp_s)
 
 hexadecimal
 
-```v oksyntax
+```v
+import strconv
+
 a1 := byte(0xff)
 b1 := i16(0xffff)
 c1 := u32(0xffffffff)
 d1 := u64(-1)
 sc3 := '%hhx %hx %x %lx'
-temp_s = strconv.v_sprintf(sc3, a1, b1, c1, d1)
+temp_s := strconv.v_sprintf(sc3, a1, b1, c1, d1)
 println(temp_s)
 ```
 
@@ -160,10 +168,12 @@ ff ffff ffffffff ffffffffffffffff
 
 hexadecimal
 
-```v oksyntax
+```v
+import strconv
+
 a2 := 125
 sc7 := '[%9x] [%9X] [%-9x] [%-9X] [%09x] [%09X]'
-temp_s = strconv.v_sprintf(sc7, a2, a2, a2, a2, a2, a2)
+temp_s := strconv.v_sprintf(sc7, a2, a2, a2, a2, a2, a2)
 println(temp_s)
 ```
 
@@ -173,13 +183,15 @@ println(temp_s)
 
 floating points
 
-```v oksyntax
+```v
+import strconv
+
 f0 := 0.312345
 f1 := 200000.0
 f2 := -1234.300e6
 f3 := 1234.300e-6
 sc4 := '[%-20.3e] [%20.3e] [%-020.3e] [%-020.3E] [%-020.3e] [%-020.3e]'
-temp_s = strconv.v_sprintf(sc4, f0, f1, f1, f1, f2, f3)
+temp_s := strconv.v_sprintf(sc4, f0, f1, f1, f1, f2, f3)
 println(temp_s)
 ```
 
@@ -189,12 +201,14 @@ println(temp_s)
 
 float automatic notations
 
-```v oksyntax
+```v
+import strconv
+
 mut ft := -1e-7
 mut x := 0
 sc8 := '[%20g][%20G]|'
 for x < 12 {
-	temp_s = strconv.v_sprintf(sc8, ft, ft)
+	temp_s := strconv.v_sprintf(sc8, ft, ft)
 	println('$temp_s\n')
 	ft = ft * 10.0
 	x++