feat(note): add circleOfFifthsDistance getter (#101)

lib/src/note/note.dart

@@ -79,6 +79,17 @@ class Note implements MusicItem, Transposable<Note> {
   PositionedNote inOctave(int octave) =>
       PositionedNote(note, accidental, octave);
 
+  /// Returns the distance in relation to the circle of fifths.
+  ///
+  /// Example:
+  /// ```dart
+  /// Note.c.circleOfFifthsDistance == 0
+  /// Note.d.circleOfFifthsDistance == 2
+  /// Note.aFlat.circleOfFifthsDistance == -4
+  /// ```
+  int get circleOfFifthsDistance =>
+      Tonality(this, TonalMode.major).keySignature.distance;
+
   /// Returns the exact fifths distance between this and [other].
   ///
   /// Example:

lib/src/tonality/key_signature.dart

@@ -28,6 +28,16 @@ class KeySignature implements Comparable<KeySignature> {
                   : Accidental.sharp,
         );
 
+  /// Returns the fifths distance of this [KeySignature].
+  ///
+  /// Example:
+  /// ```dart
+  /// const KeySignature(0).distance == 0
+  /// const KeySignature(3, Accidental.sharp).distance == 3
+  /// const KeySignature(4, Accidental.flat).distance == -4
+  /// ```
+  int get distance => accidentals * (accidental == Accidental.flat ? -1 : 1);
+
   /// Returns the [Note] that corresponds to the major [Tonality] of this
   /// [KeySignature].
   ///

test/src/note/note_test.dart

@@ -54,6 +54,26 @@ void main() {
       );
     });
 
+    group('.circleOfFifthsDistance', () {
+      test('should return the circle of fifths distance of this Note', () {
+        expect(const Note(Notes.c, Accidental.flat).circleOfFifthsDistance, -7);
+        expect(Note.gFlat.circleOfFifthsDistance, -6);
+        expect(Note.dFlat.circleOfFifthsDistance, -5);
+        expect(Note.aFlat.circleOfFifthsDistance, -4);
+        expect(Note.eFlat.circleOfFifthsDistance, -3);
+        expect(Note.bFlat.circleOfFifthsDistance, -2);
+        expect(Note.f.circleOfFifthsDistance, -1);
+        expect(Note.c.circleOfFifthsDistance, 0);
+        expect(Note.g.circleOfFifthsDistance, 1);
+        expect(Note.d.circleOfFifthsDistance, 2);
+        expect(Note.a.circleOfFifthsDistance, 3);
+        expect(Note.e.circleOfFifthsDistance, 4);
+        expect(Note.b.circleOfFifthsDistance, 5);
+        expect(Note.fSharp.circleOfFifthsDistance, 6);
+        expect(Note.cSharp.circleOfFifthsDistance, 7);
+      });
+    });
+
     group('.exactFifthsDistance()', () {
       test(
         'should return the fifths distance between this and other Note',

test/src/tonality/key_signature_test.dart

@@ -46,6 +46,16 @@ void main() {
       });
     });
 
+    group('.distance', () {
+      test('should return the fifths distance of this KeySignature', () {
+        expect(const KeySignature(7, Accidental.flat).distance, -7);
+        expect(const KeySignature(2, Accidental.flat).distance, -2);
+        expect(const KeySignature(0).distance, 0);
+        expect(const KeySignature(1, Accidental.sharp).distance, 1);
+        expect(const KeySignature(5, Accidental.sharp).distance, 5);
+      });
+    });
+
     group('.majorNote', () {
       test(
         'should return the Note that corresponds to the major Tonality of '