Usage of transactions in `:memory:` database was broken with #105

What was reported

Issue tursodatabase/libsql-client-ts#229 (closed, 11 comments): #105 regressed in memory databases when transactions are used. Once a transaction is created, the entire in memory database will be effectively discarded for subsequent db operations that the client makes.

From the regressing PR.

1. A single connection is created lazily whenever user executes a statement 2. When a transaction starts, the Transaction object takes ownership of the current transaction. 3. Subsequent queries will create a new connection.

In particular, this [line of code](https://github.com/tursodatabase/libsql-client-ts/blob/4258668bd9659e8faaf2aba9098c20ce549bd112

The verified resolution

Honest status: STILL BROKEN on main / @libsql/client 0.17.2 per a maintainer (BartWaardenburg, CONTRIBUTOR), who re-confirmed with a 17-line repro. Root cause: PR #105 made transactions take ownership of a lazily-created connection, so on :memory: DBs the in-memory database is effectively discarded for subsequent operations after a transaction. Workaround: use file::memory:?cache=shared as the URL (shared cache mode keeps one DB; introduced ~0.8/0.9 via PR #220). Caveat: closing connections behaves oddly in shared-cache mode.

Asked in gh:tursodatabase/libsql-client-ts#229 (https://github.com/tursodatabase/libsql-client-ts/issues/229): Usage of transactions in :memory: database was broken with #105. The issue report: Issue tursodatabase/libsql-client-ts#229 (closed, 11 comments): #105 regressed in memory databases when transactions are used. Once a transaction is created, the entire in memory database will be effectively discarded for subsequent db operations that the client makes.

From the regressing PR.

1. A single connection is created lazily whenever user executes a statement 2. When a transaction starts, the Transaction object takes ownership of the current transaction. 3. Subsequent queries will create a new connection.

In particular, this [line of code](https://github.com/tursodatabase/libsql-client-ts/blob/4258668bd9659e8faaf2aba9098c20ce549bd112 The verified answer: Honest status: STILL BROKEN on main / @libsql/client 0.17.2 per a maintainer (BartWaardenburg, CONTRIBUTOR), who re-confirmed with a 17-line repro. Root cause: PR #105 made transactions take ownership of a lazily-created connection, so on :memory: DBs the in-memory database is effectively discarded for subsequent operations after a transaction. Workaround: use file::memory:?cache=shared as the URL (shared cache mode keeps one DB; introduced ~0.8/0.9 via PR #220). Caveat: closing connections behaves oddly in shared-cache mode.