fix: close PGlite handle after tests to resolve exit code 100

PGlite's WASM worker kept an open async handle, causing Bun to detect
a resource leak and exit with code 100 despite all tests passing.
Adds a preload script that closes the cached client via afterAll.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

bunfig.toml

@@ -1,3 +1,4 @@
 [test]
 root = "tests/"
 timeout = 30_000
+preload = ["./tests/setup.ts"]