feat: enforce unused imports as build errors

Summary

• Implements GitLab issue #248 (closed) to make unused imports fail builds instead of just warning
• Adds workspace lint configuration with unused_imports = "deny"
• Configures all subcrates to inherit workspace lints
• Fixes existing clippy format string issues for compliance
• Fixes conditional compilation import issues discovered during CI
• Updates development documentation with new code quality requirements

Changes

• Root Cargo.toml: Added [workspace.lints.rust] section with unused_imports = "deny"
• All 11 subcrates: Added [lints] workspace = true to inherit workspace configuration
• Source files: Fixed existing clippy uninlined_format_args issues to ensure builds pass
• Conditional imports: Moved imports inside #[cfg(...)] blocks to prevent unused import errors in different build configurations
• Documentation: Updated development guides with code quality requirements and mise commands

Benefits

• Prevents code bloat: Unused imports now fail builds, preventing accumulation over time
• Consistent code quality: All workspace crates follow the same import hygiene standards
• Automated enforcement: Integrates seamlessly with existing CI/linting infrastructure
• Developer experience: Clear feedback when imports are unnecessary
• Better documentation: Developers now have clear guidance on quality requirements

Testing

• ✅ Local builds pass with cargo check --workspace
• ✅ Clippy linting passes with CI configuration
• ✅ Release mode builds tested to simulate CI conditions
• ✅ Conditional compilation scenarios verified

This extends the project's existing "warnings as errors" philosophy to import hygiene, ensuring consistent code quality across the entire workspace.

Closes #248 (closed)