docs: [#TBD] add comprehensive future improvements documentation

Add detailed module-level documentation for template_renderer.rs
outlining 10 potential improvements including:
- Comprehensive logging and monitoring
- Constants extraction for magic strings
- Input validation and error handling enhancements
- Template caching and performance optimizations
- Provider-specific logic separation for extensibility

This provides a roadmap for future maintainability and feature development.

Author: josecelano

src/stages/provision/template_renderer.rs

@@ -1,3 +1,43 @@
+//! # Template Renderer for Provision Stage
+//!
+//! This module handles OpenTofu template rendering for the provision stage of the deployment process.
+//! It manages the creation of build directories, copying template files, and processing them with
+//! variable substitution.
+//!
+//! ## Future Improvements
+//!
+//! The following improvements could enhance this module's functionality and maintainability:
+//!
+//! 1. **Add comprehensive logging** - Add debug/trace logs for each operation step (directory
+//!    creation, file copying, template processing) to improve debugging and monitoring.
+//!
+//! 2. **Extract constants for magic strings** - Create constants for hardcoded paths like "tofu",
+//!    "lxd", and file names to improve maintainability and reduce duplication.
+//!
+//! 3. **Add input validation** - Validate template names, check for empty strings, validate paths
+//!    before processing to provide early error detection and better user feedback.
+//!
+//! 4. **Improve error messages** - Make error messages more user-friendly and actionable with
+//!    suggestions for resolution, including common troubleshooting steps.
+//!
+//! 5. **Add configuration validation** - Pre-validate that required template files exist before
+//!    starting the rendering process to avoid partial failures.
+//!
+//! 6. **Extract template discovery logic** - Separate the logic for finding and listing available
+//!    templates to make it reusable and testable independently.
+//!
+//! 7. **Add progress reporting** - Add callback mechanism or progress indicators for long-running
+//!    operations to improve user experience during deployment.
+//!
+//! 8. **Improve file operations** - Add more robust file copying with better error handling and
+//!    atomic operations to prevent partial state corruption.
+//!
+//! 9. **Add template caching** - Cache parsed templates to improve performance for repeated
+//!    operations and reduce I/O overhead.
+//!
+//! 10. **Extract provider-specific logic** - Separate LXD-specific logic to make it more
+//!     extensible for other providers (Multipass, Docker, etc.) following the strategy pattern.
+
 use std::path::{Path, PathBuf};
 use thiserror::Error;