feat: add delete, context, and tx helpers

Add Delete/DeleteAffected, context-aware CRUD helpers, WithTx, ContainsCol,
and queryReturning deduplication for returning statements.

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

query.go

@@ -1,12 +1,20 @@
 package dbx
 
-import "errors"
+import (
+	"context"
+	"errors"
+)
 
 // Fetch queries the database and returns the result as a slice. If the query
 // returns no rows, it returns an empty slice and no error.
 func Fetch[T any](sqlo Queryable, stmt Statement) ([]*T, error) {
+	return FetchContext[T](context.Background(), sqlo, stmt)
+}
+
+// FetchContext is the context-aware variant of [Fetch].
+func FetchContext[T any](ctx context.Context, sqlo Queryable, stmt Statement) ([]*T, error) {
 	var result []*T
-	if err := stmt.Query(sqlo, &result); err != nil && !errors.Is(err, ErrNoRows) {
+	if err := stmt.QueryContext(ctx, sqlo, &result); err != nil && !errors.Is(err, ErrNoRows) {
 		return nil, err
 	}
 	return result, nil
@@ -15,7 +23,12 @@ func Fetch[T any](sqlo Queryable, stmt Statement) ([]*T, error) {
 // MustFetch queries the database and returns the result as a slice. If the query
 // returns no rows, it returns an empty slice and the desired error.
 func MustFetch[T any](sqlo Queryable, stmt Statement, notFoundErr error) ([]*T, error) {
-	result, err := Fetch[T](sqlo, stmt)
+	return MustFetchContext[T](context.Background(), sqlo, stmt, notFoundErr)
+}
+
+// MustFetchContext is the context-aware variant of [MustFetch].
+func MustFetchContext[T any](ctx context.Context, sqlo Queryable, stmt Statement, notFoundErr error) ([]*T, error) {
+	result, err := FetchContext[T](ctx, sqlo, stmt)
 	if err != nil {
 		return nil, err
 	}
@@ -28,7 +41,12 @@ func MustFetch[T any](sqlo Queryable, stmt Statement, notFoundErr error) ([]*T,
 // FetchOne queries the database and returns a single result. If the query
 // returns no rows, it returns nil and no error.
 func FetchOne[T any](sqlo Queryable, stmt Statement) (*T, error) {
-	result, err := Fetch[T](sqlo, stmt)
+	return FetchOneContext[T](context.Background(), sqlo, stmt)
+}
+
+// FetchOneContext is the context-aware variant of [FetchOne].
+func FetchOneContext[T any](ctx context.Context, sqlo Queryable, stmt Statement) (*T, error) {
+	result, err := FetchContext[T](ctx, sqlo, stmt)
 	if err != nil {
 		return nil, err
 	}
@@ -41,7 +59,12 @@ func FetchOne[T any](sqlo Queryable, stmt Statement) (*T, error) {
 // MustFetchOne queries the database and returns a single result. If the query
 // returns no rows, it returns nil and the desired error.
 func MustFetchOne[T any](sqlo Queryable, stmt Statement, notFoundErr error) (*T, error) {
-	result, err := MustFetch[T](sqlo, stmt, notFoundErr)
+	return MustFetchOneContext[T](context.Background(), sqlo, stmt, notFoundErr)
+}
+
+// MustFetchOneContext is the context-aware variant of [MustFetchOne].
+func MustFetchOneContext[T any](ctx context.Context, sqlo Queryable, stmt Statement, notFoundErr error) (*T, error) {
+	result, err := MustFetchContext[T](ctx, sqlo, stmt, notFoundErr)
 	if err != nil {
 		return nil, err
 	}