merge: upstream PR #2383 (en_US county provider) + fixes

Adds US county data (3143 counties across 50 states + DC) to the en_US
address provider, exposing three new methods:
  - county()            -> random county from all counties
  - county_by_state()   -> random county, optionally scoped to a state
  - county_with_state() -> 'County, State'

Paths rewritten faker/ -> faker2/ for the renamed package.

Fixes applied on top of the upstream patch:
1. counties.py: dropped the stray '"Geographic area name": []' entry, a
   leftover CSV header artifact that leaked into COUNTIES_BY_STATE. Its
   empty list made county_with_state() raise IndexError whenever that key
   was drawn. COUNTIES_BY_STATE now holds exactly 51 keys.
2. __init__.py: made the county_by_state() state argument optional
   (Optional[str] = None -> pick a random state), matching the existing
   postcode_in_state convention. Required for tests/test_factory.py::
   test_documentor, which invokes every provider method with no args.
3. Reformatted with black (line-length 120); flake8 clean.

Tests: 2742 passed, 12 skipped.

Author: jqueguiner

faker2/providers/address/en_US/__init__.py

@@ -2,6 +2,7 @@
 from typing import Optional, Tuple
 
 from ..en import Provider as AddressProvider
+from .counties import ALL_COUNTIES, COUNTIES_BY_STATE
 
 
 class Provider(AddressProvider):
@@ -447,6 +448,22 @@ class Provider(AddressProvider):
         "PW",
     )
 
+    counties = ALL_COUNTIES
+    counties_by_state = COUNTIES_BY_STATE
+
+    def county(self) -> str:
+        return self.random_element(self.counties)
+
+    def county_by_state(self, state: Optional[str] = None) -> str:
+        if state is None:
+            state = self.random_element(list(self.counties_by_state))
+        return self.random_element(self.counties_by_state[state])
+
+    def county_with_state(self) -> str:
+        state = self.random_element(list(self.counties_by_state))
+        county = self.random_element(self.counties_by_state[state])
+        return f"{county}, {state}"
+
     known_usps_abbr = states_abbr + territories_abbr + freely_associated_states_abbr
 
     military_state_abbr = ("AE", "AA", "AP")