feat(crucible): name slices only by a sure note, spelled for the song key

A slice gets a note name only when at least 60 % of up to twelve reads
across its body sit on one note; growls, pitch drops and noise get no name
rather than a wrong one. An optional song key spells names with flats in
flat keys (Eb2, not D#2).

plugins/common/dsp/tests/blocks.rs

@@ -374,5 +374,7 @@ fn note_names_parse_back() {
         assert_eq!(common_dsp::parse_note(&common_dsp::note_name(n)), Some(n));
     }
     assert_eq!(common_dsp::parse_note(" f1 "), Some(29));
+    assert_eq!(common_dsp::note_name_spelled(30, true), "Gb1");
+    assert_eq!(common_dsp::parse_note("Gb1"), Some(30));
     assert_eq!(common_dsp::parse_note("H2"), None);
 }