#134 Use big endian bit ordering and byte array paths in smt

[martti007]

No description provided.

[gemini-code-assist]

Code Review

This pull request refactors the Sparse Merkle Tree (SMT) and Sparse Merkle Sum Tree (SMST) implementations to use spec-compliant big-endian key routing instead of LSB-first routing. It replaces bigint-based path routing with direct Uint8Array operations, introducing utility functions like commonPrefixLength, regionFromKey, and getBitAtDepth, while updating node classes, error handling, and tests accordingly. The review feedback focuses on performance optimizations, suggesting byte-by-byte comparisons in commonPrefixLength and using bitwise operators (>> 3 and & 7) instead of division and modulo operations in regionFromKey, getBitAtDepth, and InclusionCertificate.

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[MastaP]

Reviewed the branch — logic checks out (I also ran dense-random-tree round-trip checks for InclusionCertificate and SplitAllocationProof locally, all green). A few cleanups and test-coverage notes inline.