Minor ffi updates for GUI app.

[NeoZ666]

Minor updates for exposing extra functionality for the GUI application w.r.t to Restore-Backup flow, Taproot Integration.

[NeoZ666]

Once this is merged, will point coinswap-ffi layer to point to the master and not my ffi branch. Can also add any taproot ffi-helper methods if needed here itself.
cc: @stark-3k @keraliss

[codecov]

Codecov Report

❌ Patch coverage is 0% with 10 lines in your changes missing coverage. Please review.
✅ Project coverage is 77.66%. Comparing base (776b75d) to head (071b553).
⚠️ Report is 51 commits behind head on master.

Files with missing lines	Patch %	Lines
src/wallet/ffi.rs	0.00%	10 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #639      +/-   ##
==========================================
+ Coverage   68.87%   77.66%   +8.79%     
==========================================
  Files          35       49      +14     
  Lines        4932    13971    +9039     
==========================================
+ Hits         3397    10851    +7454     
- Misses       1535     3120    +1585     

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