The oss-fuzz engine crashes due to stack overflow decoding a large nested structure into a interface{}. This PR limits the size of the input data, so should avoid such crashes.
* tests/fuzzers, common/bitutil: make fuzzers use correct returnvalues + remove output * tests/fuzzers/stacktrie: fix duplicate-key insertion in stacktrie (false positive) * tests/fuzzers/stacktrie: fix compilation error * tests/fuzzers: linter nits
* fuzzers: fuzzers for keystore, rlp, trie, whisper (cred to @guidovranken) * fuzzers: move fuzzers to testdata * testdata/fuzzers: documentation * testdata/fuzzers: corpus for rlp * tests/fuzzers: fixup