fix(handlers): values where omited when false and set go min version to 1.25

switching from v1 to v2 of encoding/json in the root handler to not omit
false values in the spaceapi response.
this increases the min go version to 1.25.

go.mod

@@ -1,3 +1,3 @@
 module git.hamburg.ccc.de/ccchh/spaceapid
 
-go 1.22
+go 1.25

handlers/root.go

@@ -1,7 +1,7 @@
 package handlers
 
 import (
-	"encoding/json"
+	"encoding/json/v2"
 	"log"
 	"net/http"