refactor: Fix implicit-signed-integer-truncation in cuckoocache.h

Summary:
This is a backport of core#23626

Depends on D12799

Test Plan:
With UBSAN
ninja && ninja check check-functional

Reviewers: #bitcoin_abc, Fabien

Reviewed By: #bitcoin_abc, Fabien

Differential Revision: https://reviews.bitcoinabc.org/D12812