sqldb: wire up BusyTimeout config for SQLite store

The SqliteConfig.BusyTimeout field existed but was never used — the
busy_timeout pragma was hardcoded to 5000ms. Add a busyTimeoutMs()
helper that returns the configured value or falls back to the 5000ms
default, and use it when constructing the SQLite DSN.

sqldb/sqlite.go

@@ -70,7 +70,7 @@ func NewSqliteStore(cfg *SqliteConfig, dbPath string) (*SqliteStore, error) {
 		},
 		{
 			name:  "busy_timeout",
-			value: "5000",
+			value: fmt.Sprintf("%d", cfg.busyTimeoutMs()),
 		},
 		{
 			// With the WAL mode, this ensures that we also do an