Are generated public/private keypair the most random possible? The number of possible Bitcoin private/public keypair is very strong (2^160 which is 1,461501637×10⁴⁸).

However, if the random generator is not good enough, only a subset of all that "space" could be used which would considerably break the security of Bitcoin.

That kind of problem has already happened, like that Debian bug in the OpenSSL package.

How can we be sure that random generation is done so it could generated all private/public keypair from the possible "space" ?
The source code is open take a look for yourself. I am no expert on cryptography though so I will leave the explanation of this to someone who is. This is the file that you would want to look over https://github.com/bitcoin/bitcoin/blob/master/src/key.h