feat(cpu): add {icons} format replacement for all per-core icons

Concatenates all per-core icons into a single {icons} placeholder,
so configs work across machines with different core counts without
manually specifying {icon0}{icon1}...{iconN}.

Closes #4240

man/waybar-cpu.5.scd

@@ -106,6 +106,8 @@ The *cpu* module displays the current CPU utilization.
 
 *{icon*{n}*}*: Icon for CPU core n usage. Use like {icon0}.
 
+*{icon0}{icon1}{icon2}{icon3}*: All per-core icons concatenated. Equivalent to {icon0}{icon1}...{icon*N*} but adapts to the number of cores automatically.
+
 # EXAMPLES
 
 Basic configuration:
@@ -128,6 +130,16 @@ CPU usage per core rendered as icons:
 },
 ```
 
+Automatically determine number of icons according to number of logical cores:
+
+```
+"cpu": {
+	"interval": 1,
+	"format": "{icons} {usage:>2}% ",
+	"format-icons": ["▁", "▂", "▃", "▄", "▅", "▆", "▇", "█"],
+},
+```
+
 # STYLE
 
 - *#cpu*