feat: coin control to exchange/swap send flow

[sneurlax]

closes #404

[codecov]

Codecov Report

❌ Patch coverage is 0% with 120 lines in your changes missing coverage. Please review.
✅ Project coverage is 4.83%. Comparing base (8208fe7) to head (0ff57c3).
⚠️ Report is 17 commits behind head on staging.

Files with missing lines	Patch %	Lines
lib/pages/exchange_view/send_from_view.dart	0.00%	65 Missing ⚠️
...exchange_view/exchange_step_views/step_4_view.dart	0.00%	55 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##           staging    #1374      +/-   ##
===========================================
- Coverage     4.84%    4.83%   -0.01%     
===========================================
  Files         1092     1092              
  Lines       109141   109230      +89     
===========================================
  Hits          5283     5283              
- Misses      103858   103947      +89     

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[sneurlax]

Converting to draft because I have too many open PRs ready--will take another review pass over this before re-readying it