Add define guards to avoid multi-inclusion;Limit the size of various MAXCHUNK definitions #1211

Job	Run time
check_update	1m 0s
check-ansi	2m 1s
address_ub_sanitizer	11m 2s
basic_clang	4m 10s
basic_gcc	4m 18s
memory_sanitizer	26m 16s
minimal	2m 16s
no-deprecated	4m 8s
non-caching	4m 13s
no-shared (ubuntu-latest)	3m 8s
no-shared (macos-latest)	4m 51s
ntls_address_ub_sanitizer	9m 44s
ntls_memory_sanitizer	17m 46s
threads_sanitizer	3m 39s
buildtest	6m 39s
EC_POINTs_api_test	19m 3s
enable_non-default_options	3m 34s
external-test-pyca (1.51.0, 3.9)	1m 32s
fips_and_ktls	4m 16s
legacy	3m 38s
no-legacy	4m 13s
ntls-with-fips	8m 1s
ntls-without-sm234	6m 44s
out-of-source-and-install (ubuntu-latest)	4m 19s
phe_test	35m 36s
sm2-threshold-test	42m 58s
out-of-source-and-install (macos-latest)	6m 15s
smtc_and_ntls	15m 3s
symbol_prefix-test	6m 59s
zkp-build-test	3m 20s
	4h 30m 42s

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