Complete greeting and circle_area scripts.

- A value can have many different types but a name is just a reference to a value.
- When you are filling out a form you are providing values for names. If the form
asks you to do something like "combine lines 1 and 3" your answer better not be "line 1 line 3".
- When you need to repeat a value, like the area of a circle, many times it is easier
and more efficient to save the value to a variable. It also makes code more understandable.

poetry.lock

@@ -0,0 +1,7 @@
+# This file is automatically @generated by Poetry 2.1.4 and should not be changed by hand.
+package = []
+
+[metadata]
+lock-version = "2.1"
+python-versions = ">=3.10,<4.0"
+content-hash = "7b8fc01b274bd807fb00372bbc8e138330f15ae7978ed61e180f3b17ec076725"