use better names in `plot.py`

this MR goes from

let xs = seq 0 5 | each { 2 ** $in } | wrap x
let twice = $xs | insert measurement { 2 * $in.x } | insert error { 0.1 + 0.5 * $in.x }
let square = $xs | insert measurement { $in.x ** 2 } | insert error { 1 + 1.5 * $in.x }

python scripts/plot/plot.py --title title --x-label x --y-label y --fullscreen ([
    { group: "x ^ 2", items: $square },
    { group: "2 * x", items: $twice }
] | to json)

to

let xs = seq 0 5 | each { 2 ** $in }
let twice = $xs | wrap x | insert y { 2 * $in.x } | insert e { 0.1 + 0.5 * $in.x }
let square = $xs | wrap x | insert y { $in.x ** 2 } | insert e { 1 + 1.5 * $in.x }

python scripts/plot/plot.py --title title --x-label x --y-label y --fullscreen ([
    { name: "x ^ 2", points: $square },
    { name: "2 * x", points: $twice }
] | to json)

updates the "bench" README and adds type annotations to the plot.py script.

scripts/plot/plot.py

@@ -55,7 +55,7 @@ default values have been chosen:
 
 # see [`HELP`]
 def plot(
-    data,
+    graphs,
     title: str,
     x_label: str,
     y_label: str,
@@ -66,10 +66,10 @@ def plot(
 ):
     fig, ax = plt.subplots(layout=plot_layout)
 
-    for group in data:
-        xs = [x["x"] for x in group["items"]]
-        ys = [x["measurement"] for x in group["items"]]
-        zs = [x["error"] for x in group["items"]]
+    for g in graphs:
+        xs = [x["x"] for x in g["items"]]
+        ys = [x["measurement"] for x in g["items"]]
+        zs = [x["error"] for x in g["items"]]
 
         down = [y - z for (y, z) in  zip(ys, zs)]
         up = [y + z for (y, z) in zip(ys, zs)]
@@ -81,15 +81,15 @@ def plot(
             "linewidth": None,
         }
         alpha = 0.3
-        if "style" in group:
-            custom_style = group["style"]
+        if "style" in g:
+            custom_style = g["style"]
             style["color"] = custom_style.get("color", None)
             style["marker"] = custom_style.get("line", {}).get("marker", style["marker"])
             style["linestyle"] = custom_style.get("line", {}).get("type", style["linestyle"])
             style["linewidth"] = custom_style.get("line", {}).get("width", style["linewidth"])
             alpha = custom_style.get("alpha", alpha)
 
-        ax.plot(xs, ys, label=group["group"], **style)
+        ax.plot(xs, ys, label=g["group"], **style)
         if style["color"] is None:
             ax.fill_between(xs, down, up, alpha=alpha)
         else:
@@ -119,7 +119,7 @@ if __name__ == "__main__":
     parser = argparse.ArgumentParser(
         formatter_class=argparse.RawTextHelpFormatter
     )
-    parser.add_argument("data", type=str, help=f"the actual data to show in a multibar plot\n\n{HELP}"
+    parser.add_argument("graphs", type=str, help=f"the list of graphs to plot\n\n{HELP}"
 )
     parser.add_argument("--title", "-t", type=str, help="the title of the plot")
     parser.add_argument("--x-label", "-x", type=str, help="the x label of the plot")
@@ -133,7 +133,7 @@ if __name__ == "__main__":
     plot_layout = "constrained" if args.fullscreen else None
 
     plot(
-        json.loads(args.data),
+        json.loads(args.graphs),
         args.title,
         args.x_label,
         args.y_label,