tests: Add fuzzing harness for serialization/deserialization of floating-points and integrals

Summary:

Add simple fuzzing harness for functions with floating-point parameters
(such as ser_double_to_uint64(double), etc.).

Add serialization/deserialization fuzzing for integral types.

Backport of core PR17996.

The first and last commit are not relevant to us.

Test Plan:

ninja bitcoin-fuzzers
./test/fuzz/test_runner.py <path_to_corpus>

Reviewers: #bitcoin_abc, deadalnix

Reviewed By: #bitcoin_abc, deadalnix

Differential Revision: https://reviews.bitcoinabc.org/D8249