Implement template caching for Handlebars compilation

[galligan]

Description

PR #66 mentioned template caching as a performance feature, but no caching implementation exists in the codebase.

Expected Behavior

• Compiled Handlebars templates should be cached
• Subsequent compilations of the same template should use cached version
• Cache invalidation on file changes
• Memory-efficient caching with size limits

Current Behavior

• No template caching exists
• Every compilation recompiles from scratch
• Performance degradation with multiple files

Implementation Requirements

1. LRU cache for compiled templates
2. Cache key based on file content hash
3. Configurable cache size limits
4. Cache warming for frequently used templates
5. Cache statistics for monitoring
6. Thread-safe cache operations

Performance Goals

• 50%+ speed improvement for repeated compilations
• < 100MB memory overhead for typical projects
• Sub-millisecond cache lookups

Implementation Location

• /packages/core/src/compiler/handlebars-compiler.ts
• Consider separate cache module in /packages/core/src/compiler/cache/

Test Requirements

• Test cache hit/miss scenarios
• Test cache invalidation
• Test memory limits
• Test concurrent access
• Benchmark performance improvements

Related

• PR feat: handlebars v0.2 implementation with clean architecture #66 listed this as implemented
• Critical for CLI performance
• Enables watch mode efficiency

[galligan]

Status Update

Template caching remains unimplemented but would provide significant performance benefits.

Current State

• Every compilation recompiles Handlebars templates from scratch
• No caching mechanism exists
• Performance impact is noticeable with multiple files

Proposed Implementation

• Use an LRU cache with configurable size limits
• Cache key based on file content hash
• Invalidate on file changes (watch mode integration)
• Store compiled Handlebars functions, not raw templates

Priority

Medium - This is a performance optimization that becomes more important as projects scale.