Validate invertibility of Hill cipher keys in enciphering/deciphering

[Rashad alsharpini2]

- [todo1](https://github.com/rashadalsharpini/sage/blob/28a7d0422ba718b81d555a29ec02ef07cf6d92e9/src/sage/crypto/classical.py#L1547)

- [todo2](https://github.com/rashadalsharpini/sage/blob/28a7d0422ba718b81d555a29ec02ef07cf6d92e9/src/sage/crypto/classical.py#L1573)

For the Hill cipher, encryption is defined as
- encryption c = A * M
and decryption as
- Decryption M = A^-1 * c

in these todos i have to check if A is an invertible matrix
is this correct ?

[Rashad alsharpini2]

i have created a pr related to the addressed issue