save a lot of allocations and a bit space

before

calls to allocation functions:
17.332.920 (826.085/s)
temporary allocations:
2.500.137 (14,42%, 119.156/s)

peak heap memory consumption:
570,8MB after 20.443s
peak RSS (including heaptrack overhead):
882,5MB
total memory leaked:
2,0MB (392,7kB suppressed)

now

calls to allocation functions:
18.572.056 (868.949/s)
temporary allocations:
674.882 (3,63%, 31.576/s)

peak heap memory consumption:
536,9MB after 20.776s
peak RSS (including heaptrack overhead):
843,5MB
total memory leaked:
2,0MB (392,7kB suppressed)

with some large json file fully highlighted