zcash_client_backend: Pure refactoring for note selection ergonomics.

[nuttycom]

This is a pure refactoring that should result in no functional changes.

[codecov]

Codecov Report

Attention: Patch coverage is 69.66292% with 27 lines in your changes are missing coverage. Please review.

Project coverage is 63.50%. Comparing base (2e0a300) to head (0bae47b).

Files	Patch %	Lines
zcash_client_backend/src/data_api.rs	74.28%	9 Missing ⚠️
zcash_client_sqlite/src/lib.rs	50.00%	9 Missing ⚠️
...ent_backend/src/data_api/wallet/input_selection.rs	71.42%	6 Missing ⚠️
zcash_client_backend/src/wallet.rs	81.81%	2 Missing ⚠️
zcash_client_sqlite/src/wallet/orchard.rs	0.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1271      +/-   ##
==========================================
+ Coverage   63.48%   63.50%   +0.02%     
==========================================
  Files         121      121              
  Lines       13678    13711      +33     
==========================================
+ Hits         8683     8707      +24     
- Misses       4995     5004       +9     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

[daira]

utACK