internal/app: declutter and merge small files

This should make internal/app easier to work with for the upcoming params to shim.

Signed-off-by: Ophestra <cat@gensokyo.uk>

internal/app/finalise.go

@@ -26,6 +26,17 @@ import (
 	"hakurei.app/system/wayland"
 )
 
+func newInt(v int) *stringPair[int] { return &stringPair[int]{v, strconv.Itoa(v)} }
+
+// stringPair stores a value and its string representation.
+type stringPair[T comparable] struct {
+	v T
+	s string
+}
+
+func (s *stringPair[T]) unwrap() T      { return s.v }
+func (s *stringPair[T]) String() string { return s.s }
+
 func newWithMessage(msg string) error { return newWithMessageError(msg, os.ErrInvalid) }
 func newWithMessageError(msg string, err error) error {
 	return &hst.AppError{Step: "finalise", Err: err, Msg: msg}