Integrate Shared/Critical In-Memory Logic

[dmtrshat]

Description

Ensure that shared and critical rules in the new ConfigInMemory are also processed. Similar to how we handle them in the file-based approach:

• Shared: Combine or minify shared styles.
• Critical: Combine or handle critical styles (e.g., if there’s a separate injection or special handling logic).

Acceptance Criteria

1. build_in_memory() (or the relevant method) incorporates config_in_memory.shared and config_in_memory.critical in the same manner as disk-based code does with shared/critical.
2. The returned data structure includes any generated shared or critical CSS (with an appropriate output_name).
3. Tests confirm that both shared and critical logic is invoked when the in-memory config has these sections.