zcash_protocol: Add constructors to `LocalNetwork`

[Oscar-Pepper]

Adds commonly used constructors to LocalNetwork struct.

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 0% with 11 lines in your changes are missing coverage. Please review.

Project coverage is 63.35%. Comparing base (e0227ed) to head (f668e1f). Report is 104 commits behind head on main.

:exclamation: Current head f668e1f differs from pull request most recent head 68d2add. Consider uploading reports for the commit 68d2add to get more accurate results

Files	Patch %	Lines
components/zcash_protocol/src/local_consensus.rs	0.00%	11 Missing :warning:

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1281      +/-   ##
==========================================
- Coverage   63.40%   63.35%   -0.06%     
==========================================
  Files         121      121              
  Lines       13757    13768      +11     
==========================================
  Hits         8723     8723              
- Misses       5034     5045      +11     

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