Add <cstddef> to nanobind includes. (#779) #2030

Job	Run time
Python 3.13-dev / ubuntu.latest [free-threaded]	59s
Python 3 / NVCC (CUDA 12.6.1) / ubuntu-latest	2m 4s
gcc-8 on Ubuntu 20.04	48s
Python 3.8 / ubuntu-latest	48s
gcc-9 on Ubuntu 20.04	49s
Python 3.9 / ubuntu-latest	51s
clang-8 on Ubuntu 20.04	54s
Python 3.10 / ubuntu-latest	47s
clang-9 on Ubuntu 20.04	54s
Python 3.11 / ubuntu-latest	57s
clang-10 on Ubuntu 20.04	54s
Python 3.12 / ubuntu-latest	59s
Python 3.13.0-rc.2 / ubuntu-latest	54s
Python pypy3.9-v7.3.16 / ubuntu-latest	1m 13s
Python pypy3.10-v7.3.17 / ubuntu-latest	1m 11s
Python 3.8 / windows-2022	1m 58s
Python 3.9 / windows-2022	1m 23s
Python 3.10 / windows-2022	2m 59s
Python 3.11 / windows-2022	1m 32s
Python 3.12 / windows-2022	1m 26s
Python 3.13.0-rc.2 / windows-2022	1m 58s
Python pypy3.9-v7.3.16 / windows-2022	1m 55s
Python pypy3.10-v7.3.17 / windows-2022	1m 54s
Python 3.8 / macos-13	1m 13s
Python 3.9 / macos-13	1m 19s
Python 3.10 / macos-13	1m 6s
Python 3.11 / macos-13	1m 41s
Python 3.12 / macos-13	1m 15s
Python 3.13.0-rc.2 / macos-13	1m 36s
Python pypy3.9-v7.3.16 / macos-13	1m 40s
Python pypy3.10-v7.3.17 / macos-13	1m 24s
	41m 21s

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