Adding burn field to serialized bundle

[dmidem]

This pull request introduces a change to the transaction.py script in the zcash_test_vectors repository. The modification adds a burn vector to the serialized bundle, covering both empty and non-empty burn scenarios. This change is essential for generating appropriate test vectors for the updated version of the librustzcash/zcash_primitives crate from the burn_read_write_validate branch. On this branch, a "burn" field was added into serialization and deserialization functions for the bundle.

Furthermore, in this pull request, I have refactored orchard/asset_id.py to add a derive_random_asset base function and used it to generate asset bases for the burn items.

Additionally, the Rust, JSON, and Zcash output files have been updated to reflect these changes.

[vivek-arte]

This PR is outdated, and the material is subsumed into #22 -- which includes both burn and issue additions to the transaction ID and sighash generation