ci: add cargo clippy with deny warnings

[Divine-mercyx]

Summary

• Make the CI clippy job actually enforce -D warnings by removing the crate-level #![allow(warnings)] in dongle-smartcontract/src/lib.rs.
• Fix or scope the remaining contract lints (unused imports, needless mut, dead helpers, too_many_arguments) so cargo clippy -p dongle-contract --target wasm32-unknown-unknown -- -D warnings passes.
• Keep clippy in CI and run it with --all-features so new warnings fail the lint job.

Type of Change

• Bug fix (non-breaking change fixing an issue)
• New feature (non-breaking change adding functionality)
• Breaking change (fix or feature causing existing functionality to change)
• Refactoring / Documentation update

Changes Made

• Removed crate-wide #![allow(warnings)] from the contract crate.
• Applied targeted clippy/rustc fixes in the contract sources.
• Scoped remaining intentional cases with #[allow(clippy::too_many_arguments)] and #[allow(dead_code)].
• Routed get_project_region / get_project_integrity_hash through ProjectRegistry instead of duplicating storage reads.
• Strengthened the CI clippy command with --all-features.

Acceptance Criteria

• CI runs cargo clippy with deny warnings.
• allow(warnings) in lib.rs is removed rather than left crate-wide.
• Remaining lints are fixed or scoped to the specific items that need them.

Testing

• cargo clippy -p dongle-contract --target wasm32-unknown-unknown --all-features -- -D warnings
• cargo test -p dongle-contract region_and_integrity

Closes #511

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