Feature: Add tests to ensure the field layout in ValidatorHistoryEntry never changes

[buffalu]

Is your feature request related to a problem? Please describe.
During a previous refactor, the engineers of this program accidentally re-arranged fields in the ValidatorHistoryEntry and corrupted data. It was fixed, but easy to do again in the future.

Describe the solution you'd like
Add tests to ensure the field layout of the ValidatorHistoryAccount doesn't change if fields are added, removed, or changed.

[hydrogenbond007]

@buffalu gib issue

[hydrogenbond007]

Update -> Adding assert fields in the test but getting error "no rules expected this token in macro call"

mod layout_tests {
use super::*;
use static_assertions::assert_fields;
use std::mem::{align_of, size_of};

#[test]
fn test_validator_history_layout() {
    assert_fields!(
        ValidatorHistory,
        struct_version: u32,
        vote_account: Pubkey,
        index: u32,
        bump: u8,
        _padding0: [u8; 7],
        last_ip_timestamp: u64,
        last_version_timestamp: u64,
        _padding1: [u8; 232],
        history: CircBuf,
    );

    assert_eq!(size_of::<ValidatorHistory>(), 65848);
    assert_eq!(align_of::<ValidatorHistory>(), 8);
}

}