Address all math issues reported by soteria

None of these should have been a real issue.

programs/voter-stake-registry/src/instructions/log_voter_info.rs

@@ -54,7 +54,12 @@ pub fn log_voter_info(ctx: Context<LogVoterInfo>, deposit_entry_begin: u8) -> Re
             end_timestamp: (lockup.kind != LockupKind::Constant).then(|| end_ts),
             vesting: lockup.kind.is_vesting().then(|| VestingInfo {
                 rate: deposit.amount_initially_locked_native / periods_total,
-                next_timestamp: end_ts - (periods_left - 1) * lockup.kind.period_secs(),
+                next_timestamp: end_ts.saturating_sub(
+                    periods_left
+                        .saturating_sub(1)
+                        .checked_mul(lockup.kind.period_secs())
+                        .unwrap(),
+                ),
             }),
         });
 

programs/voter-stake-registry/src/state/deposit_entry.rs

@@ -342,7 +342,10 @@ impl DepositEntry {
             vested_amount <= self.amount_initially_locked_native,
             InternalProgramError
         );
-        self.amount_initially_locked_native -= vested_amount;
+        self.amount_initially_locked_native = self
+            .amount_initially_locked_native
+            .checked_sub(vested_amount)
+            .unwrap();
         self.lockup.remove_past_periods(curr_ts)?;
         require!(self.vested(curr_ts)? == 0, InternalProgramError);
         Ok(())

programs/voter-stake-registry/src/state/lockup.rs

@@ -113,7 +113,11 @@ impl Lockup {
         if curr_ts < self.start_ts {
             return self.periods_total();
         }
-        Ok((self.seconds_left(curr_ts) + period_secs - 1) / period_secs)
+        Ok(self
+            .seconds_left(curr_ts)
+            .checked_add(period_secs.saturating_sub(1))
+            .unwrap()
+            / period_secs)
     }
 
     /// Returns the current period in the vesting schedule.

programs/voter-stake-registry/src/state/registrar.rs

@@ -26,7 +26,11 @@ const_assert!(std::mem::size_of::<Registrar>() == 5 * 32 + 4 * 120 + 8 + 1 + 31)
 
 impl Registrar {
     pub fn clock_unix_timestamp(&self) -> i64 {
-        Clock::get().unwrap().unix_timestamp + self.time_offset
+        Clock::get()
+            .unwrap()
+            .unix_timestamp
+            .checked_add(self.time_offset)
+            .unwrap()
     }
 
     pub fn voting_mint_config_index(&self, mint: Pubkey) -> Result<usize> {