Add support for interpolation in context names

src/spectator/context.cr

@@ -4,6 +4,11 @@
 # This type is intentionally outside the `Spectator` module.
 # The reason for this is to prevent name collision when using the DSL to define a spec.
 abstract class SpectatorContext
+  # Evaluates the contents of a block within the scope of the context.
+  def eval
+    with self yield
+  end
+
   # Produces a dummy string to represent the context as a string.
   # This prevents the default behavior, which normally stringifies instance variables.
   # Due to the sheer amount of types Spectator can create

src/spectator/dsl/groups.cr

@@ -137,7 +137,7 @@ module Spectator::DSL
                  what.is_a?(NilLiteral) %}
         {{what}}
       {% elsif what.is_a?(StringInterpolation) %}
-        {% raise "String interpolation isn't supported for example group names" %}
+        {{@type.name}}.new.eval { {{what}} }
       {% else %}
         {{what.stringify}}
       {% end %}