Add after_compile hook for component extensions

[jsolas]

Following up on the conversation with @joelhawksley and @fsateler in this comment, this PR introduces a minimal extension point in the ViewComponent::Compiler.

What are you trying to accomplish?

This PR creates a minimal extension point for ViewComponent::Compiler to enable "sub-templates" functionality through a dedicated gem. The sub-templates gem will work by overriding the after_compile hook, receiving the compiled component, and then searching for additional template files (e.g., header.html.erb, row.html.erb) in the component's directory to generate corresponding call_* methods with explicit locals validation.

What approach did you choose and why?

I chose to implement a simple after_compile instance method hook as suggested by @joelhawksley. This approach is:

Simple and Direct: Following Joel's preference for simplicity over sophisticated callback systems
Easy to Document: A straightforward method override pattern that's familiar to Rails developers
Zero Overhead: No performance impact when the hook isn't overridden
Non-invasive: Doesn't modify ViewComponent's core compilation logic
Extensible: Components can easily override the method to add custom post-compilation behavior
The implementation uses allocate to call the instance method without triggering the component's constructor, avoiding the complexity of handling initialization arguments.

Anything you want to highlight for special attention from reviewers?

• The hook is implemented as an instance method (not class method) to provide maximum flexibility for extensions while avoiding Ruby inheritance edge cases
• Currently uses @component.allocate.after_compile to avoid constructor complexity, but I'm uncertain if this is the most elegant solution. Open to suggestions for alternative approaches that don't require allocate.

[jsolas]

Friendly ping @joelhawksley! Any chance to get feedback on this? Happy to make changes if needed