perf(graph): eliminate heavy allocations by substituting KnowledgeGraph clones with BorrowedGraph for json serialization

temp_setup.lua

@@ -0,0 +1,6 @@
+local buf = vim.fn.bufnr('server/src/handlers_v2/graph.rs')
+if buf == -1 then
+    vim.cmd('e server/src/handlers_v2/graph.rs')
+    buf = vim.api.nvim_get_current_buf()
+end
+return vim.api.nvim_buf_get_name(buf)