Implement teardown contract for ESPCrypto

[zekageri]

Summary

• add static lifecycle APIs to ESPCrypto: deinit() and isInitialized()
• centralize global runtime state (policy, nonce-guard cache, NVS init cache, boot counter) and reset it in idempotent deinit()
• mark runtime initialization in policy-gated and cache-backed paths while keeping overhead low
• add teardown lifecycle tests for pre-init safety, repeated deinit, and deinit -> use -> deinit re-init flow
• update README and basic_hash_and_aes example to show explicit teardown usage

Testing

• not run locally (pio and cmake are not available in this environment)