refactor: move the RX pulse decoder into PulseDecoder

The decoding of the time between received edges into frame bits moves out
of Transceiver::handleReceive unchanged into decodePulse(), with the RTS
timings and the receive buffer type. It stays in IRAM on the ESP32 and is
now covered by native tests that feed it the edges sendFrame() produces
for 56 and 80-bit first frames and repeats, a glitch and a broken pulse.

handleReceive keeps the noise guard, the edge timing and the RX queue.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

src/PulseDecoder.h

@@ -0,0 +1,53 @@
+#ifndef PULSE_DECODER_H
+#define PULSE_DECODER_H
+#include <stdint.h>
+#include <string.h>
+
+// Turns the time between edges of a received RTS transmission into frame
+// bits.  Runs in the receive interrupt, so it stays in IRAM on the ESP32, and
+// is kept free of the radio so it can be unit tested on the PC
+// (pio test -e native).
+
+// Half an RTS bit in us.  A bit is two symbols with an edge in the middle.
+#define SYMBOL 640
+
+#define MAX_TIMINGS 300
+
+typedef enum {
+    waiting_synchro = 0,
+    receiving_data = 1,
+    complete = 2
+} t_status;
+
+struct somfy_rx_t {
+    void clear() {
+      this->status = t_status::waiting_synchro;
+      this->bit_length = 56;
+      this->cpt_synchro_hw = 0;
+      this->cpt_bits = 0;
+      this->previous_bit = 0;
+      this->waiting_half_symbol = false;
+      memset(this->payload, 0, sizeof(this->payload));
+      memset(this->pulses, 0, sizeof(this->pulses));
+      this->pulseCount = 0;
+    }
+    t_status status;
+    uint8_t bit_length = 56;
+    uint8_t cpt_synchro_hw = 0;
+    uint8_t cpt_bits = 0;
+    uint8_t previous_bit = 0;
+    bool waiting_half_symbol;
+    uint8_t payload[10];
+    unsigned int pulses[MAX_TIMINGS];
+    uint16_t pulseCount = 0;
+};
+
+enum class PulseResult : uint8_t {
+  glitch,  // Too short to be a symbol.  The caller times the next edge from the last one.
+  more,    // Taken, the frame isn't complete yet.
+  frame    // rx holds a complete frame.
+};
+// Feeds the time since the previous edge to rx.
+PulseResult decodePulse(somfy_rx_t &rx, uint32_t durationUs);
+#endif
+