Expand docs, add Rust Astryx crate, and harden CI

[MeridianAlgo-Developer]

Motivation

• Improve repository documentation and provide concrete, reproducible example outputs for the hash primitive so users can validate behavior and follow usage patterns.
• Harden and modernize CI to validate both the Python prototype and the Rust implementation across relevant toolchains and versions.
• Provide guidance and notes for blockchain-oriented integration and security hardening without claiming production-grade security.

Description

• Rewrote and expanded README.md with usage examples, deterministic example digests (e.g., "Astryx" and "block_header_height_124") and quick-start instructions for both Python and Rust usage.
• Upgraded GitHub Actions workflow to .github/workflows/ci.yml with a Python matrix (3.10/3.11/3.12), a Rust fmt + test job, a docs-consistency job, workflow_dispatch, concurrency cancellation, pip/cargo caching, and a CLI smoke test.
• Added new documentation pages: docs/CI.md (CI guide) and docs/BLOCKCHAIN_SECURITY.md (domain separation, canonicalization, migration and audit guidance).
• Introduced a Rust crate implementation and test harness with src/lib.rs, src/walk.rs, src/compress.rs, and src/tests.rs, plus Cargo.toml/Cargo.lock, backward-compatible aliases (gaqwh*), and a target/ entry in .gitignore, while removing committed Python bytecode.

Testing

• Ran cargo fmt --all -- --check which completed successfully.
• Ran cargo test --all-targets --all-features which passed (7 tests, 0 failures).
• Ran the Python unit test suite python -m unittest discover -s tests -q which passed (13 tests OK).

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