Also:
- Make DEFAULT_MAX_SIG_CACHE_SIZE into constexpr
DEFAULT_MAX_SIG_CACHE_BYTES to utilize the compile-time integer
arithmetic overflow checking available to constexpr.
- Fix comment (MiB instead of MB) for DEFAULT_MAX_SIG_CACHE_BYTES.
- Pass in max_size_bytes parameter to InitS*Cache()
- Fix possible integer truncation and add a comment.
[META] I've kept the integer types as int64_t in order to not introduce
unintended behaviour changes, in the next commit we will make
them size_t.
This is a partial backport of core#25527
https://github.com/bitcoin/bitcoin/pull/25527/commits/41c5201a90bbc2893333e334e8945759ef24e7dd
Depends on D15737
Backport note: Bitcoin ABC has two separate options for script cache size and sig cache size, while Core uses a single value and assigns half for each cache.