feat(i2c): implement callback-free I2C slave driver for ESP32-C3/C6 (#5709)

* feat(i2c): implement callback-free I2C slave driver for ESP32-C3/C6

* refactor(i2c): extract slave driver polling steps and simplify Sealed impl

* fix(examples): add .cargo/config.toml to i2c slave example to fix CI build

* refactor: address I2C slave PR comments and fix CI link checks

* refactor(i2c): expose slave module as unstable_module