feat: Same layout between country/language pickers (settings)

[g123k]

Hi everyone!

This PR changes the language picker in the settings (I will change later the one for the edit mode).
The code is also shared between country and language pickers.

Video: https://github.com/user-attachments/assets/808530d6-1db0-4fd0-8777-0142a283348e

Settings

Harmonized titles: "Select a country" vs "Your country"

Shared UI

Loading state

When countries/languages were loading, the placeholder had a different height -> no more issue

Onboarding

A circle arrow is added on the onboarding

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 0.27100% with 368 lines in your changes missing coverage. Please review.

Project coverage is 6.14%. Comparing base (4d9c7fc) to head (ee87e29).
Report is 674 commits behind head on develop.

Files with missing lines	Patch %	Lines
...ets/selector_screen/smooth_screen_list_choice.dart	0.86%	114 Missing ⚠️
...eferences/language_selector/language_selector.dart	0.00%	94 Missing ⚠️
...preferences/country_selector/country_selector.dart	0.00%	53 Missing ⚠️
...lector_screen/smooth_screen_selector_provider.dart	0.00%	44 Missing ⚠️
.../language_selector/language_selector_provider.dart	0.00%	38 Missing ⚠️
...es/country_selector/country_selector_provider.dart	0.00%	15 Missing ⚠️
...references/user_preferences_language_selector.dart	0.00%	3 Missing ⚠️
...preferences/user_preferences_country_selector.dart	0.00%	2 Missing ⚠️
...pp/lib/generic_lib/widgets/languages_selector.dart	0.00%	1 Missing ⚠️
...references/user_preferences_currency_selector.dart	0.00%	1 Missing ⚠️
... and 3 more

Additional details and impacted files

@@            Coverage Diff             @@
##           develop   #6231      +/-   ##
==========================================
- Coverage     9.54%   6.14%   -3.41%     
==========================================
  Files          325     460     +135     
  Lines        16411   26848   +10437     
==========================================
+ Hits          1567    1650      +83     
- Misses       14844   25198   +10354     

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