feat(be): add bis and insz

[mikeryancodes]

This work adds Belgium BIS and INSZ.

The BIS appears to be quite similar to the NN, except that the DOB month portion of the identifier is incremented by either 20 or 40.

I tried and could not find what 'BIS' stands for online.

This refactors the NN code so it can use an optional function for getting the DOB from the original number, and then uses that to implement BIS.

It appears that an INSZ number is either a BIS or NN, I wrote this validator in terms of the other two taking an 'invalid checksum' error over an 'invalid format' error if we get different errors as noted.

[commit-lint[bot]]

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mikeryancodes

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