Refactor pagination system with flexible ordering support

This commit overhauls the pagination system to support flexible ordering
beyond the default created_at timestamp:

- Change CursorKey from fixed byte array to structured object with ID and Value
- Add OrderField and OrderDirection types to support different sorting options
- Update SQLFragment to dynamically generate SQL based on field and direction
- Modify cursor navigation logic to consider custom ordering
- Simplify Position type to use string constants instead of numeric values
- Update Page struct to include reference to Cursor

These changes allow paginated queries to be ordered by different fields
(created_at, updated_at, name) in either ascending or descending order
while maintaining consistent cursor-based pagination behavior.

Signed-off-by: gearnode <bryan@frimin.fr>

pkg/page/page.go

@@ -16,7 +16,7 @@ package page
 
 type (
 	Paginable interface {
-		CursorKey() CursorKey
+		CursorKey(orderBy OrderField) CursorKey
 	}
 
 	PageInfo struct {
@@ -25,8 +25,9 @@ type (
 	}
 
 	Page[T Paginable] struct {
-		Info *PageInfo
-		Data []T
+		Info   *PageInfo
+		Cursor *Cursor
+		Data   []T
 	}
 )
 
@@ -73,7 +74,7 @@ func NewPage[T Paginable](data []T, c *Cursor) *Page[T] {
 			edges = edges[0 : len(edges)-1]
 		}
 
-		if c.Key != nil && *c.Key == firstFromData.CursorKey() {
+		if c.Key != nil && c.Key.String() == firstFromData.CursorKey(c.OrderBy.Field).String() {
 			pi.HasPrev = true
 		}
 
@@ -97,7 +98,7 @@ func NewPage[T Paginable](data []T, c *Cursor) *Page[T] {
 			edges = edges[1:]
 		}
 
-		if c.Key != nil && *c.Key == firstFromData.CursorKey() {
+		if c.Key != nil && c.Key.String() == firstFromData.CursorKey(c.OrderBy.Field).String() {
 			pi.HasNext = true
 		}
 
@@ -109,7 +110,8 @@ func NewPage[T Paginable](data []T, c *Cursor) *Page[T] {
 	}
 
 	return &Page[T]{
-		Info: pi,
-		Data: edges,
+		Info:   pi,
+		Cursor: c,
+		Data:   edges,
 	}
 }