track nSigChecks in CheckInputs
Summary:
This makes CheckInputs do the following:
- If sigchecks are found in cache, return them.
- If cache miss and checks are not deferred, then accumulate the total of inputs' sigchecks, store them in cache if requested, and then finally return those.
- If cache miss and checks are deferred, return 0 sigchecks.
Test Plan: ninja check
Reviewers: #bitcoin_abc, deadalnix
Reviewed By: #bitcoin_abc, deadalnix
Maniphest Tasks: T704
Differential Revision: https://reviews.bitcoinabc.org/D5126