refactor: Change extension entrypoint to sphinxnotes.snippet (2nd)

[SilverRainZ]

Replace #31, with non-golbal import :D

#34:
import time:       190 |      20072 | sphinxnotes.snippet.cli
#v2
import time:       338 |      41215 | sphinxnotes.snippet.cli
#31
import time:       320 |     481846 | sphinxnotes.snippet.cli