Mark unstable APIs

[MabezDev]

We need to mark APIs we're not stabilizing as such. These are all APIs except following:

• esp_hal::init
• esp_hal::Config
  • just CpuClock, everything else should be unstable
• clocks - Stabilizing CpuClock #2663
• peripheral - Evaluate the Peripheral and Peripheral ref module #2661
• peripherals - Ensure the PAC crates and other private crates are never exposed publicly #2525
• prelude - Remove the prelude #2660
• gpio - Stable driver: GPIO #2492 GPIO unstable items #2693
• uart - Stable driver: UART #2495
• spi::master::Spi - Stable driver: SPI master #2494
• i2c::master::I2c - Stable driver: I2C master #2493
• interrupt - only InterruptHandler, and Priority (though we need to decide if we expose Priority::None, see: Make set_interrupt panic free #2760)
  • Required for Add inherent set_interrupt_handler method to drivers #2905
• esp-hal-macros, will also be stabilized (1.0)
  • Only #[main] will be stable though - macros: Add #[main] macro #2920

We should just have one feature unstable. I thought about a feature per driver/module but in reality enabling all or just a few won't make a difference to the end user, if we make a breaking change to an unstable API it will only affect users who are actively using that API, not just because its available.

How we implement unstable is being tracked here: #2498