mmrs: sim pin/puk operations

[cachebag]

implement sim card pin/puk unlock and management.

lock state detection

check Modem.State for Locked state, then query Modem.UnlockRequired to determine lock type:

• MM_MODEM_LOCK_SIM_PIN — needs pin
• MM_MODEM_LOCK_SIM_PUK — needs puk + new pin
• MM_MODEM_LOCK_SIM_PIN2, MM_MODEM_LOCK_SIM_PUK2 — secondary pin/puk

api

pub async fn unlock_pin(&self, pin: &str) -> Result<()>;
pub async fn unlock_puk(&self, puk: &str, new_pin: &str) -> Result<()>;
pub async fn set_pin_enabled(&self, pin: &str, enabled: bool) -> Result<()>;
pub async fn change_pin(&self, old: &str, new: &str) -> Result<()>;

error handling

map mm errors to typed variants:

• wrong pin → ModemError::WrongPin
• pin required → ModemError::PinRequired
• puk required → ModemError::PukRequired
• sim not inserted → ModemError::NoSim

retry tracking

Sim.UnlockRetries property gives remaining attempts before lockout. surface this in error messages or as a query method.