Stop parsing the radix tree if the callback function returns false

Summary: This diff lets the callsite decide to continue or stop the tree traversal at each leaf. Returning true continue the loop, and returning false stops it.

Test Plan:

ninja check

Reviewers: #bitcoin_abc, deadalnix

Reviewed By: #bitcoin_abc, deadalnix

Subscribers: deadalnix

Differential Revision: https://reviews.bitcoinabc.org/D11459