> rpc: Fix implicit-integer-sign-change in verifychain
> Avoid implicit-integer-sign-change in VerifyLoadedChainstate
The UB in VerifyLoadedChainstate was inadvertently fixed in D14614 when the `unsigned int` parameters became `int64_t`.
This backport just adds the test coverage in rpc_blochain.py
This is a backport of core#24403 and core#24347