Add support for HPKE #1037

Job	Run time
build_python_27 (ubuntu-22.04, no)	45s
build_python_27 (ubuntu-22.04, yes)	43s
build_python_27 (windows-latest, no)	17s
build_python_27 (windows-latest, yes)	16s
test_c_linux (1, x32)	1m 16s
python_no_gil	46s
test_c_linux (0, x64)	56s
test_c_windows (x64)	36s
test_c_linux (1, x64)	55s
test_c_windows (win32)	1m 10s
build (3.7, yes, ubuntu-22.04)	39s
test_c_linux (0, x32)	1m 11s
build (3.8, no, ubuntu-22.04)	34s
mypy	15s
build (3.7, no, ubuntu-22.04)	38s
build (3.9, no, ubuntu-22.04)	21s
build (3.10, yes, ubuntu-22.04)	28s
build (3.11, yes, ubuntu-22.04)	33s
build (3.13, yes, ubuntu-22.04)	31s
build (3.8, yes, ubuntu-22.04)	32s
build (3.9, yes, ubuntu-22.04)	22s
build (3.13, yes, macos-13)	1s
build (3.12, no, ubuntu-22.04)	22s
build (3.13, no, ubuntu-22.04)	23s
build (3.11, no, ubuntu-22.04)	30s
build (3.10, no, ubuntu-22.04)	23s
build (3.12, yes, ubuntu-22.04)	31s
build (pypy3.9, no, ubuntu-latest)	26s
build (3.13, yes, ubuntu-22.04-arm)	1s
build (3.13, yes, windows-latest)	1s
build (pypy2.7, no, ubuntu-latest)	26s
build (3.13, no, windows-latest)	26s
	17m 14s

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