Implement binary search for power start / end search

[jonashoechst]

The signal extraction on the spectrogram relies on a linear search.

pyradiotracking/radiotracking/analyze.py

Lines 175 to 196 in a6e953d

	# loop down until threshold is undershot
	start = ti
	start_min = 0 if self._spectrogram_last is None else -len(self._spectrogram_last[0])
	while start > start_min:
	if start < 0:
	power = self._spectrogram_last[fi, start]
	else:
	power = fft[start]
	if power < self.signal_threshold:
	break
	start -= 1
	# loop up until threshold is undershot
	end = ti
	while end < len(fft):
	if fft[end] < self.signal_threshold:
	ti_skip = end
	break
	end += 1

When using binary search, a significant performance gain in low signal thresholds can be expected.