Implement parallel provider compilation

[galligan]

Description

PR #66 mentioned parallel provider compilation as a performance optimization, but the implementation compiles providers sequentially.

Expected Behavior

// Should compile all providers in parallel
const results = await Promise.all(
  providers.map(provider => compileForProvider(source, provider))
);

Current Behavior

• Providers are compiled sequentially
• No parallelization exists
• Slower compilation for multiple providers

Implementation Requirements

1. Parallel compilation using Promise.all
2. Configurable concurrency limits
3. Error handling for partial failures
4. Progress reporting for long compilations
5. Resource pooling for memory efficiency
6. Graceful degradation under load

Performance Goals

• 3-4x speedup for 4+ providers
• Linear scaling up to CPU core count
• Memory usage < 2x sequential mode
• No race conditions or data corruption

Implementation Location

• Core compilation orchestration logic
• May need worker pool implementation

Test Requirements

• Test parallel execution
• Test error handling in parallel mode
• Test concurrency limits
• Test resource cleanup
• Benchmark performance gains
• Test data isolation between parallel compilations

Related

• PR feat: handlebars v0.2 implementation with clean architecture #66 claimed this was implemented
• Critical for multi-provider projects
• Improves developer experience

[galligan]

Status Update

This issue is still relevant and needs implementation. The parallel compilation feature would significantly improve performance for multi-provider projects.

Current State

• Sequential compilation is working correctly
• No parallelization exists yet
• This is a performance optimization, not a blocker

Next Steps

1. Implement Promise.all() for parallel provider compilation
2. Add configurable concurrency limits
3. Add proper error handling for partial failures
4. Benchmark performance improvements

This should be prioritized after core functionality is stable.