Test occasionally fail as the VIES API seem to rate limit the requests

[JanmanX]

======================================================================
1) ERROR: check_vat_number('..', country_code='..')
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   Traceback (most recent call last):
    tests/test_validators.py line 257 in test_dk__country_code
      check_vat_number(vat_number, country_code)
    pyvat/__init__.py line 212 in check_vat_number
      country_code)
    pyvat/registries.py line 133 in check_vat_number
      raise ServerError(fault_code)
   ServerError: ServerError: MS_MAX_CONCURRENT_REQ
   -------------------- >> begin captured logging << --------------------
   urllib3.connectionpool: DEBUG: Starting new HTTP connection (1): ec.europa.eu:80
   urllib3.connectionpool: DEBUG: http://ec.europa.eu:80 "POST /taxation_customs/vies/services/checkVatService HTTP/1.1" 200 None
   --------------------- >> end captured logging << ---------------------
-----------------------------------------------------------------------------

[cyrilballagny]

Hi! I try to request this service too with some batch queries but I am facing the same limit. Do you have any idea about the rate limit/SLA of VIES? I can't manage to find any details related to this.
Regards