[fix][fiscobcos][offchain] stabilize account and native provider loading

[fengjy73]

• Add privateKey to FISCOBCOSConfig.
• Prefer the configured private key when creating the BBC transaction keypair, with optional 0x prefix support.
• Handle native crypto initialization failures explicitly and restore thread interrupt state.
• Support optional provider library loading via fiscobcos.providers.lib or FISCOBCOS_PROVIDERS_LIB.
• Guard provider library loading so it only runs once across BBC instances.
• Use stable ABI constants: AuthMsg.ABI, SDPMsg.ABI, and PtcHub.ABI.
• Use AuthMsg.ABI consistently for event decoding and recvPkgFromRelayer.
• Release FISCO resources on shutdown with client.stop(), client.destroy(), and sdk.stopAll().