Minor enhancements to custom LDLT implementations #784

Job	Run time
ubuntu-clang14	10m 59s
ubuntu-gcc11	10m 26s
format	1m 50s
bazel	8m 55s
clang-tidy	32s
osx-clang	8m 19s
ubuntu-build-documentation	1m 25s
ubuntu-clang14-sanitizers (address-undefined-leak, ./ci/run_address_sanitizer_tests.sh)	13m 48s
ubuntu-clang14-sanitizers (thread, ./ci/run_thread_sanitizer_tests.sh)	12m 59s
	1h 9m 13s

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