Adding additional logging when overflow occurs in calculate_stake_rew…

[roryharr]

Problem

Currently unwrap is used during calculate_stake_rewards, this lead to a lack of logging when an overflow occurs.

It might be better to take an action other than panic!, but it matches the current code and it's not clear to me what other action should be taken.

Summary of Changes

Additional logs during overflow calculations during calculate_stake_rewards
No change of functionality, validated through new unit tests.

Fixes #

[mergify]

The Firedancer team maintains a line-for-line reimplementation of the
native programs, and until native programs are moved to BPF, those
implementations must exactly match their Agave counterparts.
If this PR represents a change to a native program implementation (not
tests), please include a reviewer from the Firedancer team. And please
keep refactors to a minimum.