sqlite improvements (#1965)

* use direct blocking calls for SQLite in `sqlx_macros`
    * this also ensures the database is closed properly, cleaning up tempfiles
* don't send `PRAGMA journal_mode` unless set
    * this previously defaulted to WAL mode which is a permanent setting
      on databases which doesn't necessarily apply to all use-cases
    * changing into or out of WAL mode acquires an exclusive lock on the database
      that can't be waited on by `sqlite3_busy_timeout()`
    * for consistency, `sqlx-cli` commands that create databases will still
      create SQLite databases in WAL mode; added a flag to disable this.
* in general, don't send `PRAGMA`s unless different than default
    * we were sending a bunch of `PRAGMA`s with their default values just to enforce
      an execution order on them, but we can also do this by inserting empty slots
      for their keys into the `IndexMap`
* add error code to `SqliteError` printout
* document why `u64` is not supported

sqlx-cli/src/database.rs

@@ -11,6 +11,12 @@ pub async fn create(connect_opts: &ConnectOpts) -> anyhow::Result<()> {
     let exists = crate::retry_connect_errors(connect_opts, Any::database_exists).await?;
 
     if !exists {
+        #[cfg(feature = "sqlite")]
+        sqlx::sqlite::CREATE_DB_WAL.store(
+            connect_opts.sqlite_create_db_wal,
+            std::sync::atomic::Ordering::Release,
+        );
+
         Any::create_database(&connect_opts.database_url).await?;
     }