feat: ae trn validation added (#40)

UAE has TRN(Tax Registration Number) to submit vat. A person can
have TRN to submit VAT on invoiced income. Business needs to have TRN to be
registered.

ref: https://www.cleartax.com/ae/trn-verification-uae

Author: mdamire

stdnum/ae/__init__.py

@@ -0,0 +1,3 @@
+from stdnum.ae import trn as vat  # noqa: F401
+from stdnum.ae import trn as business_tin  # noqa: F401
+from stdnum.ae import trn as personal_tin  # noqa: F401

stdnum/ae/trn.py

@@ -0,0 +1,50 @@
+# trn.py - functions for handling UAE TRN numbers
+# ref:
+#   https://www.cleartax.com/ae/trn-verification-uae
+#   https://tax.gov.ae/en/services/vat.registration.aspx
+
+"""TRN (Tax Registration Number)
+
+The TRN is a 15 digit number.
+
+>>> validate('123456789012345')
+'123456789012345'
+>>> validate('1234-5678901-2345')
+'123456789012345'
+>>> validate('1234567890123456')
+Traceback (most recent call last):
+    ...
+stdnum.exceptions.InvalidLength: The number has an invalid length.
+"""
+
+import re
+
+from stdnum.exceptions import *
+from stdnum.util import clean
+
+
+_trn_re = re.compile(r'^\d{15}$')
+
+
+def compact(number):
+    """Convert the number to the minimal representation. This strips the
+    number of any valid separators and removes surrounding whitespace."""
+    return clean(number, ' -').strip()
+
+
+def validate(number):
+    """Check if the number is a valid TRN. This checks the length and format."""
+    number = compact(number)
+    if len(number) != 15:
+        raise InvalidLength()
+    if not _trn_re.match(number):
+        raise InvalidFormat()
+    return number
+
+
+def is_valid(number):
+    """Check if the number is a valid TRN."""
+    try:
+        return bool(validate(number))
+    except ValidationError:
+        return False

tests/test_ae_trn.doctest

@@ -0,0 +1,30 @@
+>>> from stdnum.ae import trn
+
+>>> trn.validate('123456789012345')
+'123456789012345'
+>>> trn.is_valid('123456789012345')
+True
+>>> trn.validate('1234-5678901-2345')
+'123456789012345'
+>>> trn.is_valid('1234-5678901-2345')
+True
+>>> trn.validate(' 1234-5678901-2345 ')
+'123456789012345'
+>>> trn.is_valid(' 1234-5678901-2345 ')
+True
+>>> trn.validate(' 1234-5678901-2 345 ')
+'123456789012345'
+>>> trn.is_valid(' 1234-5678901-2 345 ')
+True
+>>> trn.validate('1234567890123456')
+Traceback (most recent call last):
+    ...
+stdnum.exceptions.InvalidLength: The number has an invalid length.
+>>> trn.is_valid('1234567890123456')
+False
+>>> trn.validate('12345678901234A')
+Traceback (most recent call last):
+    ...
+stdnum.exceptions.InvalidFormat: The number has an invalid format.
+>>> trn.is_valid('1234-567890123456')
+False