Credit in a full-reserve system is created when individuals (banks, businesses, etc) extend credit at their own expense. The difference to the current fractional reserve system is that the bank can only lend out of funds they genuinely control (ie haven't promised to hold ready for withdrawal).

When I buy a certificate of deposit I lose the claim on my money. This is an extension of credit by me to the bank. It is not inflationary because I lose the funds. Fractional reserve credit creation is inflationary because I continue to claim the funds (and so does whoever borrowed them).

Credit ends with money payment, while money does not end.

So no, mining companies do not create credit.

Credit, currency and money are all different things. I don't doubt that digital currencies will be used in future. I very much doubt that such a thing as digital money is even logically possible.