Implement teardown contract for esp-memoryMonitor

[zekageri]

Summary

• harden deinit() to release monitor-owned container capacity via container reinitialization
• preserve teardown contract semantics (deinit() idempotent + pre-init safe, destructor delegates to deinit(), isInitialized() remains public)
• add lifecycle teardown tests covering pre-init deinit, idempotent deinit, re-init after teardown, runtime-state cleanup, and destructor behavior
• document explicit teardown usage in README and examples/manual_sampling (serial x deinit / i init)

Validation

• pio --version (not available in this environment)
• arduino-cli version (not available in this environment)

Notes

• no backward-compatibility aliases were introduced