Add Nu6 support

Add support for NU6.1 version on ZCash

Summary by CodeRabbit

• New Features

  • Added support for the latest Zcash NU6 and NU6_1 network branches.

• Improvements

  • More robust construction and decoding of script-based transaction outputs for improved transaction handling.

• Chores

  • Updated underlying libraries to align with recent protocol and API revisions.

• Tests

  • Updated SAPLING decrypt test fixture and associated test data.

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