95969bc58ae0cd928e536d7cb8541de93e8c7205 test: added fuzz coverage to consensus/merkle.cpp (kevkevinpal)
Pull request description:
### Summary
This adds a new fuzz target "merkle" which adds fuzz coverage to `consensus/merkle.cpp`
I can also add this to an existing fuzz target if that is preferable
Before:

After:

ACKs for top commit:
marcofleon:
ReACK 95969bc58ae0cd928e536d7cb8541de93e8c7205
Prabhat1308:
ACK [`95969bc`](95969bc58a)
maflcko:
lgtm ACK 95969bc58ae0cd928e536d7cb8541de93e8c7205
achow101:
ACK 95969bc58ae0cd928e536d7cb8541de93e8c7205
Tree-SHA512: e1fe8b69444733516bfa6cf2adaa199fde4c7c5582b7b908408f9313ed0f2e8cb803d27d707a1716d49606d5eaef8c1e722990bbc3cffc30fa91fe73d2233e9d