fix(core): clear foreign root handlers by default

[PakitoSec]

Summary

• clear all root handlers during init_logger() by default so Logurich stays the single logging sink and foreign formatters do not receive Rich-backed record attributes unexpectedly
• add the clear_handlers=False opt-out for runtimes that must keep existing root handlers attached
• document the root-handler ownership behavior in the README and v1 migration guide, and bump the package version to 1.0.1

Testing

• add pytest coverage for default handler clearing, the clear_handlers=False opt-out, forced reconfiguration cleanup, and ensuring foreign handlers do not observe Logurich records when clearing is enabled