* Add failing tests
* Fix stake split
* Calculate split rent-exempt-reserve and use
* Add comment in rent.rs
* Add tests for edge cases when splitting to larger accounts, and reject overflow splits
* Reframe InsufficientFunds checks in terms of lamports var
* Test hardening review comments
(cherry picked from commit 4c5f345798
)
Co-authored-by: Tyera Eulberg <teulberg@gmail.com>