Malachite v0.9.0 — Performance & Rate Limiting Overhaul

I've completely redesigned the rate limiting and batching logic in Malachite to maximize throughput while respecting PDS quotas.

Dynamic Batching: The tool now uses server-learned rate limits to dynamically adjust batch sizes and pacing in real-time.
Recovery Mode: Added a "recovery mode" with adaptive wait times for when quotas are critically low.
Credential Security: Implemented SHA-512 based auto-saving for credentials and standardized all local storage paths to ~/.malachite/.
Validation: Added unit tests for Spotify imports, CSV parsing, and sync utilities to ensure reliability during high-speed operations.