Unified Internal Utilities (Parser, CSSOptimizer)

[dmtrshat]

Description

Refactor the parser and optimizer calls (if necessary) so both the file-based and in-memory code paths reuse as much logic as possible:

• Parser: Add a new method, e.g., parse_classes_from_string(content: &str) so that the in-memory path doesn’t rely on reading files.
• Optimizer: Already likely works on a &str basis, so confirm it’s reused seamlessly.

Acceptance Criteria

1. Parser logic can handle either reading from file-based input paths or directly from string slices (for the new in-memory config).
2. Duplicated logic is minimized (no separate copy-paste for disk vs. memory).
3. Confirm code compiles and tests pass for both usage modes.