First pass at uniformed types, specs and docs

- spec public functions (skipping controllers, views, live views and
components)
- use types instead of explanations in docs
- remove redundant docs
- fix typos

lib/music_library/record_sets/record_set.ex

@@ -16,6 +16,9 @@ defmodule MusicLibrary.RecordSets.RecordSet do
     timestamps(type: :utc_datetime)
   end
 
+  @type t :: %__MODULE__{}
+
+  @spec changeset(t() | Ecto.Changeset.t(), map()) :: Ecto.Changeset.t()
   def changeset(record_set, attrs) do
     record_set
     |> cast(attrs, [:name, :description])
@@ -24,6 +27,11 @@ defmodule MusicLibrary.RecordSets.RecordSet do
     |> validate_length(:description, max: 10_000)
   end
 
+  @spec count_by_status(t()) :: %{
+          collected: non_neg_integer(),
+          wishlisted: non_neg_integer(),
+          total: non_neg_integer()
+        }
   def count_by_status(record_set) do
     record_set.items
     |> Enum.frequencies_by(fn item ->

lib/music_library/record_sets/record_set_item.ex

@@ -17,6 +17,9 @@ defmodule MusicLibrary.RecordSets.RecordSetItem do
     timestamps(type: :utc_datetime)
   end
 
+  @type t :: %__MODULE__{}
+
+  @spec changeset(t() | Ecto.Changeset.t(), map()) :: Ecto.Changeset.t()
   def changeset(record_set_item, attrs) do
     record_set_item
     |> cast(attrs, [:position])