Implement in-memory cache for modules

[konard]

🎯 Summary

Implements in-memory caching for modules to significantly improve performance by avoiding redundant file operations, as requested in issue #27.

📋 Changes Made

• Module Caching: Added moduleCache Map to store imported modules by their resolved path
• Built-in Caching: Added builtinCache Map to cache built-in modules by module:environment key
• baseUse Enhancement: Modified to check cache before importing and store results after processing
• Built-in Resolver Enhancement: Modified to cache built-in module results to avoid repeated imports
• Comprehensive Testing: Added tests/cache.test.mjs with 5 test cases covering different caching scenarios
• Demo Example: Added examples/cache-demo.mjs to demonstrate caching performance improvements

🧪 Test Coverage

All new caching functionality is thoroughly tested:

• ✅ Module cache returns same instance on repeated calls
• ✅ Built-in module cache works correctly
• ✅ Different modules are cached separately
• ✅ Same object reference returned for cached modules
• ✅ Built-in cache works with both regular and node: prefixed imports

🔧 Technical Implementation

Module Caching

// In-memory cache for loaded modules to avoid redundant file operations
const moduleCache = new Map();

export const baseUse = async (modulePath) => {
  // Check if module is already cached
  if (moduleCache.has(modulePath)) {
    return moduleCache.get(modulePath);
  }
  // ... import and process module ...
  // Cache the processed module for future use
  moduleCache.set(modulePath, processedModule);
  return processedModule;
};

Built-in Module Caching

// Cache for built-in modules to avoid redundant imports
const builtinCache = new Map();

// Create cache key including environment for built-in modules
const cacheKey = `${moduleName}:${environment}`;
if (builtinCache.has(cacheKey)) {
  return builtinCache.get(cacheKey);
}

🚀 Performance Impact

• First Import: Normal loading time (file system + processing)
• Subsequent Imports: Near-instant return of cached module
• Memory Usage: Minimal increase due to caching references
• Behavior: 100% backward compatible - no breaking changes

📁 Files Modified

• use.mjs - Added caching to module and built-in resolvers
• use.js - Applied same caching changes for browser compatibility
• use.cjs - Applied same caching changes for CommonJS compatibility
• tests/cache.test.mjs - New comprehensive test suite
• examples/cache-demo.mjs - New demo script

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Fixes #27

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