Implement Galileo E1B I/NAV navigation decoding

tests/navigation/test_symbol_sync.py

@@ -0,0 +1,35 @@
+from __future__ import annotations
+
+import numpy as np
+
+from galileo_rx.navigation.e1b_prompt_stream import E1BPromptEpoch
+from galileo_rx.navigation.e1b_symbol_sync import E1BSymbolSynchronizer
+
+
+def _epoch(index: int, sign: int, *, slip: bool = False) -> E1BPromptEpoch:
+    start = index * 16
+    prompt = sign * np.exp(1j * 0.37)
+    return E1BPromptEpoch(
+        1, start, start + 16, float(prompt.real), float(prompt.imag), 0.0, 1000.0, 0.0,
+        50.0, True, True, slip, False, True,
+    )
+
+
+def test_symbol_sync_preserves_global_polarity_ambiguity() -> None:
+    truth = np.asarray([1, -1] * 12, dtype=np.int8)
+    synchronizer = E1BSymbolSynchronizer(minimum_axis_epochs=4, minimum_confidence=0.9)
+    symbols = synchronizer.process_many([_epoch(i, int(-value)) for i, value in enumerate(truth)])
+    hard = np.asarray([item.hard_value for item in symbols[4:]], dtype=np.int8)
+    # Either polarity is valid here; page synchronization resolves it later.
+    expected_bits = (truth[4:] > 0).astype(np.int8)
+    assert np.array_equal(hard, expected_bits) or np.array_equal(hard, 1 - expected_bits)
+    assert all(not item.inverted for item in symbols)
+
+
+def test_cycle_slip_invalidates_and_restarts_axis_lock() -> None:
+    sync = E1BSymbolSynchronizer(minimum_axis_epochs=3, minimum_confidence=0.1)
+    symbols = [sync.process(_epoch(i, 1, slip=i == 5)) for i in range(10)]
+    assert symbols[5].valid is False
+    assert symbols[6].valid is False
+    assert symbols[7].valid is True
+    assert sync.loss_count == 1