ble_client 8 digit PIN

**Describe the problem you have/What new integration you would like**
Extend the ble_client to support 8 digit PINs.

**Please describe your use case for this integration and alternatives you've tried:**
Pax Calima uses 8 digit PIN for authentication. I would like to add Pax Calima to the HA and for that I would need a BT proxy that connects to the Pax Calima with the PIN.

**Additional context**
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Start by locating the ble_client implementation and its current PIN handling. Reproduce the Pax Calima authentication use case and inspect how an 8-digit PIN should be accepted without affecting existing support. The issue names no file or test, so completion is verifying a successful connection with an 8-digit PIN.

Written by the indexing model from the issue text.