Fix loading large non file-visiting buffers + simplification of the implementation #23

Job	Run time
test (ubuntu-latest, 27.2, false)	36s
test (ubuntu-latest, 28.2, false)	37s
test (ubuntu-latest, 29.3, false)	44s
test (macos-latest, 28.2, false)	1m 32s
test (macos-latest, 29.3, false)	1m 27s
test (windows-latest, 27.2, false)	50s
test (windows-latest, 28.2, false)	1m 11s
test (windows-latest, 29.3, false)	1m 18s
test (ubuntu-latest, snapshot, true)	31s
test (macos-latest, snapshot, true)	1m 14s
test (windows-latest, snapshot, true)	54s
	10m 54s

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