Additions needed for Orchard batch scanning

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 0% with 2 lines in your changes are missing coverage. Please review.

Project coverage is 80.59%. Comparing base (3d79ba4) to head (ff7287e).

Files	Patch %	Lines
src/note/nullifier.rs	0.00%	2 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #419 +/- ## ========================================== - Coverage 80.64% 80.59% -0.06% ========================================== Files 30 30 Lines 3152 3154 +2 ========================================== Hits 2542 2542 - Misses 610 612 +2 ```

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