Make the global console instance thread-safe

[hbisneto]

Problem: The global console instance mutates internal state (_fore, _back, _styles) without locks, causing race conditions in concurrent writes

Why it matters: Multi-threaded CLIs can interleave styles, producing garbled output.

Proposed solution: Wrap state mutations in Console.call and style methods with a threading.Lock. Document that the global instance is now thread-safe; recommend per-instance Console for maximum performance.

Notes: Measure overhead; keep lock granularity minimal to avoid blocking single-threaded use.