Add uart

[IvanArkhipov1999]

Note

Adds a new uart feature with APIs and ESP32 UART2/IO support, centralizes peripheral init, introduces a UART echo example, updates CI, and does minor refactors/tests tweaks.

• Core API:
  • Add uart feature in Cargo.toml and public getters get_uart2/get_io; call setup_uart() from init_system() when enabled.
  • Extend PortTrait with type Uart2Type, type IoType, and methods setup_uart(), get_uart2(), get_io().
• ESP32 (xtensa/riscv32):
  • New peripherals module centralizing esp_hal::init and storing raw handles (TIMG0/1, RNG, RADIO_CLK, WIFI, UART2, GPIO, IO_MUX).
  • Refactor hardware_timer to use centralized peripherals.
  • Update network to pull peripherals from new module.
  • Implement uart module providing UART2/Io acquisition and one-time init.
• Other Ports:
  • MIPS64: add uart stub module and wire types/methods.
  • Mok: add mock uart module and wire types/methods.
• Examples & CI:
  • Add examples/rust-examples/xtensa-esp32/uart (UART echo) with tooling/config.
  • CI: add xtensa-esp32-rust-example-uart job to build/format the new example.
• Scheduler/Tests:
  • Preemptive: replace tight infinite loops with spin_loop, add Default for PreemptiveTaskManager, allow attributes for lints.
  • Tests: gate cooperative tests to skip under preemptive feature.
• Misc:
  • Minor cleanups: boolean simplifications, #[allow(static_mut_refs)] and similar lints.

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