Add support for Czech/Slovak IČ - company registration number

[PavelPancocha]

Just 8 digits.

Example: https://or.justice.cz/ias/ui/rejstrik-firma.vysledky?subjektId=47718&typ=PLATNY&sp=H4sIAAAAAAAAAKtWykvMTU0JSCwCUiWpRcVKVtHVStmplUpWQJmq1DIlHaWyxJzSVCD%252F6MLs%252FJRE%250D%250AhcTSknyl2thaAOBvbwI7AAAA%250D%250A

Example: 00177041, could be formatted as 001 77 041

[dbartenstein]

@PavelPancocha is there any official API in the Czech Republic where the company registration number could be validated? See example for Germany:

python-stdnum/stdnum/de/handelsregisternummer.py

Line 328 in 6cbb9bc

def check_offeneregister(number, timeout=30): # pragma: no cover (not part of normal test suite)

[arthurdejong]

Is there a relation to the DIČ number (which is included in python-stdnum already)?

Btw, see https://github.com/arthurdejong/python-stdnum/blob/master/CONTRIBUTING.md#adding-number-formats for what information would be useful when adding a new number format.

[PavelPancocha]

In most cases the IČ(O) (its the same thing) is just the DIČ without CZ prefix, but can be different - mainly for physical persons. Also if you are now VAT payer, you don't provide the VAT on invoices, it is only used internally with tax-office.

You can use this official API to get info about specific number: https://ares.gov.cz/swagger-ui/#/ekonomicke-subjekty-szr/vratEkonomickySubjektSzr

[DMZ22]

Opened #504 for this — adds stdnum.cz.ico and stdnum.sk.ico (8-digit IČO with the modulo-11 check digit). To @arthurdejong's question: for a legal entity the IČO is the same number as the Czech DIČ without the CZ prefix, so the Czech module reuses the check-digit algorithm already in cz/dic, and the Slovak module delegates to the Czech one (mirroring sk/rc → cz/rc). Included 21 real Czech and 21 real Slovak numbers as regression tests.