fix: WillPopScope migration

[sneurlax]

Migrate the deprecated WillPopScope widget to PopScope across the app. Simple barrier dialogs become canPop: false/true. Cases that ran side effects or conditionally gated the pop move that work into onPopInvokedWithResult.

[codecov]

Codecov Report

❌ Patch coverage is 1.76263% with 836 lines in your changes missing coverage. Please review.
✅ Project coverage is 4.84%. Comparing base (8208fe7) to head (ab8a128).
⚠️ Report is 11 commits behind head on staging.

Files with missing lines	Patch %	Lines
lib/pages/coin_control/coin_control_view.dart	0.00%	219 Missing ⚠️
...p_views/sub_views/stack_restore_progress_view.dart	0.00%	152 Missing ⚠️
...in_selection/exchange_currency_selection_view.dart	0.00%	61 Missing ⚠️
...ages/paynym/subwidgets/desktop_paynym_details.dart	0.00%	43 Missing ⚠️
lib/pages/cashfusion/fusion_progress_view.dart	0.00%	33 Missing ⚠️
lib/pages/churning/churning_progress_view.dart	0.00%	30 Missing ⚠️
...y_phrase_view/new_wallet_recovery_phrase_view.dart	0.00%	29 Missing ⚠️
...wallet_views/select_wallet_for_sol_token_view.dart	0.00%	28 Missing ⚠️
lib/pages/paynym/dialogs/paynym_details_popup.dart	0.00%	24 Missing ⚠️
...add_wallet_views/select_wallet_for_token_view.dart	0.00%	23 Missing ⚠️
... and 33 more

Additional details and impacted files

@@           Coverage Diff            @@
##           staging    #1375   +/-   ##
========================================
  Coverage     4.84%    4.84%           
========================================
  Files         1092     1092           
  Lines       109141   109069   -72     
========================================
+ Hits          5283     5286    +3     
+ Misses      103858   103783   -75     

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