fix: correct paging parameter logic and add paging options

- fix bug where `pageNumber` and `pageSize` were swapped during default
initialization in `apps.go`.
- fix bug in `pagingRequest.go` where `ToParams` mapped keys to the
incorrect struct fields.
- add `ForPageNumber` and `WithPageSize` functional options to allow
custom paging configuration.
- enhance `Apps` endpoint tests to verify that `pageNumber` and
`pageSize` query parameters are correctly passed to the API.
- add test case for verifying non-default paging options.

apps.go

@@ -21,8 +21,8 @@ type App struct {
 
 func (p *AppsEndpoint) Get(ctx context.Context, pagingOpts ...PagingOption) (Page[App], error) {
 	pagingRequest := &PagingRequest{
-		pageSize:   1,
-		pageNumber: 50,
+		pageNumber: 1,
+		pageSize:   50,
 	}
 
 	for _, opt := range pagingOpts {