Add fuzz tests in cqlvalue with random data

[martin-sucha]

Currently fuzz tests for CQL values like FuzzCqlValueInt32 test that data == deserialize(serialize(data)). However, these kinds of tests are unlikely to find issues like panics because of missing bounds checks when parsing data, since they only try to parse valid data.

For example, CqlValue.AsStringMap seems that it will panic if the CQLValue.Value field does not have enough bytes (although I haven't tried running the function yet).

Consider adding fuzz tests that do deserialize(random bytes) and test that the parsing functions never panic for cql values as well.