refactor: split gpodder repository and the sqlite data store implementation into separate crates

The complete separation of concerns via the gpodder repository allows us
to cleanly separate the server from the gpodder specification. This
paves the way for a later Postgres implementation of the data store.

gpodder_sqlite/migrations/2025-02-23-095541_initial/down.sql

@@ -0,0 +1,10 @@
+drop table episode_actions;
+
+drop table device_subscriptions;
+
+drop table sync_groups;
+
+drop table devices;
+
+drop table sessions;
+drop table users;

gpodder_sqlite/migrations/2025-02-23-095541_initial/up.sql

@@ -0,0 +1,86 @@
+create table users (
+    id integer primary key not null,
+
+    username text unique not null,
+    password_hash text not null
+);
+
+create table sessions (
+    id bigint primary key not null,
+
+    user_id bigint not null
+        references users (id)
+        on delete cascade,
+
+    last_seen bigint not null,
+
+    unique (id, user_id)
+);
+
+create table devices (
+    id integer primary key not null,
+
+    device_id text not null,
+    user_id bigint not null
+        references users (id)
+        on delete cascade,
+    sync_group_id bigint
+        references sync_groups (id)
+        on delete set null,
+
+    caption text not null,
+    type text not null,
+
+    unique (user_id, device_id)
+);
+
+create table sync_groups (
+    id integer primary key not null
+);
+
+create table device_subscriptions (
+    id integer primary key not null,
+
+    device_id bigint not null
+        references devices (id)
+        on delete cascade,
+
+    podcast_url text not null,
+
+    time_changed bigint not null,
+    deleted boolean not null default false,
+
+    unique (device_id, podcast_url)
+);
+
+create table episode_actions (
+    id integer primary key not null,
+
+    user_id bigint not null
+        references users (id)
+        on delete cascade,
+    -- Can be null, as the device is not always provided
+    device_id bigint
+        references devices (id)
+        on delete set null,
+
+    podcast_url text not null,
+    episode_url text not null,
+
+    time_changed bigint not null,
+
+    timestamp bigint,
+    action text not null,
+    started integer,
+    position integer,
+    total integer,
+
+    -- Position should be set if the action type is "Play" and null otherwise
+    check ((action = "play") = (position is not null)),
+
+    -- Started and position can only be set if the action type is "Play"
+    check (action = "play" or (started is null and position is null)),
+
+    -- Started and position should be provided together
+    check ((started is null) = (total is null))
+);