Massive improvements to NanoVDB #1658

Job	Run time
linux-nanovdb:cxx:g++-Release	7m 56s
windows-nanovdb (x64-windows-static, Release, -A x64 -G \"Visual Studio 17 2022\" -DOPENVDB_CORE_...	22m 47s
linux-nanovdb:cxx:g++-Debug	6m 57s
windows-nanovdb (x64-windows-static, Debug, -A x64 -G \"Visual Studio 17 2022\" -DOPENVDB_CORE_SH...	24m 28s
linux-nanovdb:cxx:clang++-Release	7m 59s
windows-nanovdb (x64-windows, Release, -A x64 -G \"Visual Studio 17 2022\" -DOPENVDB_CORE_STATIC=...	24m 44s
linux-nanovdb:cxx:clang++-Debug	6m 17s
windows-nanovdb (x64-windows, Debug, -A x64 -G \"Visual Studio 17 2022\" -DOPENVDB_CORE_STATIC=OFF)	27m 55s
macos-nanovdb (macos-11, clang++, Release)	1h 13m 2s
nanovdb-lite	2m 52s
macos-nanovdb (macos-11, clang++, Debug)	1h 5m 35s
	4h 30m 32s

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