refactor: split dbx package into domain files

Reorganize monolithic dbx.go and utility.go into focused files by
concern, add package doc.go, and gitignore coverage.out.

Co-authored-by: Cursor <cursoragent@cursor.com>

interfaces.go

@@ -0,0 +1,54 @@
+package dbx
+
+import (
+	"context"
+	"database/sql"
+
+	"github.com/go-jet/jet/v2/qrm"
+)
+
+// SQLOFunc is a function that returns a *sql.DB pointer.
+type SQLOFunc = func() *sql.DB
+
+// Queryable interface is an SQL driver object that can execute SQL statements
+// for Jet.
+type Queryable interface {
+	qrm.Queryable
+	Query(string, ...any) (*sql.Rows, error)
+}
+
+// Executable interface is an SQL driver object that can execute SQL statements
+// for Jet.
+type Executable interface {
+	qrm.Executable
+	Exec(string, ...any) (sql.Result, error)
+}
+
+// ExecutableTx interface is an SQL driver object that implements the Executable
+// interface and can also begin a transaction.
+type ExecutableTx interface {
+	Executable
+	Begin() (*sql.Tx, error)
+}
+
+// QueryExec interface is an SQL driver object that can execute SQL statements for Jet
+// and query results.
+type QueryExec interface {
+	Queryable
+	Executable
+}
+
+// QueryExecTx interface is an SQL driver object that can execute SQL statements for
+// Jet, query results, and begin a transaction.
+type QueryExecTx interface {
+	Queryable
+	ExecutableTx
+}
+
+// Statement is a common Jet statement for all SQL operations.
+type Statement interface {
+	Query(db qrm.Queryable, destination any) error
+	QueryContext(ctx context.Context, db qrm.Queryable, destination any) error
+	Exec(db qrm.Executable) (sql.Result, error)
+	ExecContext(ctx context.Context, db qrm.Executable) (sql.Result, error)
+}