Add idfxx_lora and idfxx_sx126x components for LoRa radio

[cleishm]

Summary

Adds LoRa radio support as two new components:

idfxx_lora — chip-agnostic LoRa radio abstraction:

• Abstract lora::radio base class using the non-virtual-interface pattern: public non-virtual try_*/throwing method pairs with protected do_* hooks that drivers override privately. Chip-agnostic validation (payload length, positive duty-cycle periods) lives in the base.
• Three data-path styles: blocking calls (transmit/receive/scan_channel, composed in the base over the async hooks), future-based one-shot operations (start_transmit, single-shot start_receive into a caller buffer, and start_channel_scan return idfxx::future and need no event loop), and event streams for continuous/duty-cycled receive, with typed events (tx_done, rx_done, crc_error, cad_done, preamble_detected) posted on an idfxx::event_loop.
• Semantic modulation/packet types (spreading factor, bandwidth, coding rate, ramp time) that drivers map to chip register encodings.
• constexpr helpers that need no hardware: time_on_air() implementing the Semtech air-time equation, and rx_duty_cycle_for() computing listen/sleep windows for duty-cycled receive that cannot miss a packet.

idfxx_sx126x — driver for the Semtech SX126x family (SX1261/SX1262/SX1268) over idfxx_spi:

• Per-variant PA configuration with full output-power range validation, including the SX1261's +15 dBm case (high-duty-cycle PA row with a +14 SetTxParams byte, per DS table 13-21).
• Datasheet errata workarounds: BW500 TX modulation quality (§15.1), antenna-mismatch TX clamp (§15.2), boosted-RX gain refresh across duty-cycle sleep windows; software-managed timeouts avoid the chip's RTC timeout errata.
• Optional TCXO via DIO3 (with full recalibration), DIO2-as-RF-switch or external rxen/txen switch GPIOs, LDO/DC-DC regulator selection, and warm/cold sleep and RC/XOSC standby refinements as typed-enum overloads of the base interface.
• DIO1 ISR feeding a worker task that drains chip IRQs, completes per-operation futures, and posts events. Each async operation completes through its own heap-allocated latch, so outstanding futures stay valid across cancellation (standby/sleep) and driver teardown.
• Image calibration per frequency band, a low-level opcode/register escape hatch, and four standalone examples (transmit_beacon, receive_log, ping_pong, duty_cycle_listener).

Both components ship Unity tests with compile-time verification of register encodings, PA/power tables, and air-time and duty-cycle window calculations against datasheet reference values, and are listed in the top-level README component table.

idfxx_core 1.1.1 — fixes the flags<E> bitwise operators (|, &, ^, -, ~), which failed to compile for enums with an underlying type smaller than int: integer promotion made the braced construction of the result a narrowing error. The SX126x driver's 16-bit irq_flag bitfield is the first such use. New static_asserts in the flags tests cover each operator with a uint16_t-based enum.