ignore command (#59)

* New table `ignored_users` and queries

* Update sqlx to 0.8

* Implement `ignore` command and add needed hooks

youmubot-db-sql/migrations/20250327105109_ignored_users.sql

@@ -0,0 +1,7 @@
+-- Add migration script here
+
+CREATE TABLE ignored_users (
+  id BIGINT NOT NULL PRIMARY KEY,
+  username TEXT NOT NULL UNIQUE,
+  ignored_since DATETIME NOT NULL DEFAULT (DATETIME('now'))
+);