test(audit): add entry hash fuzz harness

[brentthomas248]

Closes #1701

Summary:

• add a fuzz-tests harness for audit entry_hash determinism
• cover operation, optional string, optional amount, and optional hash field sensitivity
• verify adjacent audit-chain entries stay consistent and tampering is detected

Tests:

• PATH="$HOME/.cargo/bin:$PATH" rustfmt --edition 2021 --check quicklendx-contracts/src/test_fuzz_audit_hash.rs
• git diff --check
• PATH="$HOME/.cargo/bin:$PATH" cargo test -p quicklendx-contracts --features fuzz-tests test_fuzz_audit_hash -- --nocapture (blocked by unrelated current-base compile errors before the new harness compiles: duplicate bench module, duplicate compute_yield definitions, missing idempotency/address_summary module declarations, and missing InvalidLedgerSequence match)