feat(engine): export fuzz harness scaffolds (#415)

[edehvictor]

Closes #415

Changes

• adds a new sanctifier fuzz CLI command for generating native fuzz harness scaffolds
• introduces a reusable core generator that inspects Soroban contract source and discovers public entrypoints
• exports afl.rs and honggfuzz.rs templates with contract metadata, entrypoint summaries, and Soroban-specific TODO guidance
• supports generating a single backend or both backends, with configurable output directory and overwrite protection
• adds CLI tests covering help output, dual-harness generation, and engine-specific generation

Testing

• cargo fmt --package sanctifier-core --package sanctifier-cli
• cargo test -p sanctifier-cli (blocked in this environment: missing MSVC link.exe)

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