feat: add merkletreeparent util functions

[wregulski]

Description of Changes

Context:

This package was adopted from:

go-bc and it's used in SPV-Wallet repositories for example for calculating merged BUMP.

This pull request introduces new functionality for calculating Merkle Tree parents, along with corresponding tests. The changes include adding three new functions to the transaction package and creating unit tests to ensure their correctness.

New functionality for Merkle Tree calculations:

• transaction/merkletreeparent.go: Added three functions for calculating Merkle Tree parents: MerkleTreeParentStr, MerkleTreeParent, and MerkleTreeParentBytes. ([transaction/merkletreeparent.goR1-R54](https://github.com/bitcoin-sv/go-sdk/pull/53/files#diff-8fa5befb90358e9aa105c88a75bbd58837f0e73bc02c9cf501a1c24b141ff3f1R1-R54))

Unit tests for new functions:

• transaction/merkletreeparent_test.go: Added unit tests for MerkleTreeParentStr and MerkleTreeParent to verify their correctness. ([transaction/merkletreeparent_test.goR1-R32](https://github.com/bitcoin-sv/go-sdk/pull/53/files#diff-d0ddc5fccb41065ddee86d95499c66536b1a262fee9c3e0dcf9168a4460b2a39R1-R32))

Linked Issues / Tickets

No references to specific tasks (maintenance/feedback).

• I have added new unit tests
• All tests pass locally
• I have tested manually in my local environment

Checklist:

• I have performed a self-review of my own code
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have updated CHANGELOG.md with my changes
• I have run npm run doc and npm run lint one final time before requesting a review