Fix ExifTool geolocation parsing for custom path templates

[vesaias]

Summary

Two related fixes for the ExifTool reverse-geolocation flow added in #481 / #505 so country/city/state placeholders resolve correctly end-to-end when used inside %custom templates.

Verified end-to-end against an iPhone photo geotagged in Chivay, Peru:

• Before: 2022-03/Chivay/... — country slot filled with city name.
• After: 2022-03 Peru/... — country resolves correctly from the [Directory] location=%country alias.

Changes

1. elodie/geolocation.py — accept both prefixed and bare exiftool keys. is_exiftool_available, exiftool_coordinates_by_name, and exiftool_place_name only checked for ExifTool:GeolocationCity/etc., but exiftool returns bare GeolocationCity/etc. when the -G group flag isn't in effect. A new _geolocation_field helper tries both forms.

2. elodie/filesystem.py — expand sub-key aliases inside %custom templates. get_dynamic_path for custom recursively dispatched each %foo token but passed the literal %foo as the mask, ignoring the [Directory] config alias. With a config like

   [Directory]
   date=%Y-%m
   location=%country
   custom=%date %location
   full_path=%custom

   %location resolved to place_name['default'] (the city, since exiftool_place_name sets default to the most-specific field) instead of expanding via the location=%country alias. The custom resolver now looks up sub-keys in [Directory] and passes the alias value when dispatching, mirroring the top-level path resolver.

Tests

• 4 new tests in geolocation_test.py cover both bare and prefixed Geolocation* key forms in is_exiftool_available, exiftool_coordinates_by_name, and exiftool_place_name (mocking ExifTool so they're network-free and deterministic).
• 1 new test in filesystem_test.py (test_get_folder_path_custom_template_expands_location_alias) exercises the %custom → %location → %country expansion chain with a mocked place_name.

All other tests pass except for 7 pre-existing failures on master that depend on a live MapQuest key (test_get_folder_path_with_location, test_get_folder_path_with_album_and_location_fallback, test_get_folder_path_with_custom_path, test_get_folder_path_with_with_more_than_two_levels, test_get_folder_path_with_location_and_title, test_process_file_with_location, test_process_file_with_location_and_title) — verified to fail identically against master before this change.

Test plan

• pytest elodie/tests/geolocation_test.py — 27 passed, 2 skipped, 5 pre-existing env failures unchanged
• pytest elodie/tests/filesystem_test.py — new test passes; same 7 pre-existing failures as master
• Live import dry-run with [Directory] location=%country config: *.JPG (Chivay/Peru GPS) lands at out/2022-03 Peru/...

[CLAassistant]

All committers have signed the CLA.