Strict addition with a signed integer. Computes `self + rhs`, panicking if overflow occurred.
# Panics
## Overflow behavior
This function will always panic on overflow, regardless of whether overflow checks are enabled.
# Examples
Basic usage:
```
# use ::exint::primitive::*;
# ::exint::uint! {
assert_eq!(1_u24.strict_add_signed(2_i24), 3_u24);
# }
```
The following panics because of overflow:
```should_panic
# use ::exint::primitive::*;
# ::exint::uint! {
let _ = 1_u24.strict_add_signed(-2_i24);
# }
```
```should_panic
# use ::exint::primitive::*;
# ::exint::uint! {
let _ = (u24::MAX - 2_u24).strict_add_signed(3_i24);
# }
```