chore: use NotImplementedError instead of ...

Also I should probably lock Ruff with dev dependency
rather than always installing the latest version in the CI.

ricecake/hangul/compose.py

@@ -3,12 +3,12 @@
 
 def compose(cho: str, jung: str, jong: str | None) -> str:
     """Composes Choseong, Jungseong, and Jongseong into a Syllable."""
-    ...
+    raise NotImplementedError
 
 
 def decompose(syl: str) -> tuple[str, str, str | None]:
     """Decomposes a Syllable into Choseong, Jungseong, and Jongseong."""
-    ...
+    raise NotImplementedError
 
 
 # FEAT: decompose composite Jaum and Moum into tuple of str

ricecake/hangul/convert.py

@@ -3,19 +3,19 @@
 
 def jamo_to_compat_jamo(c: str, /) -> str | None:
     """Maps a Jamo character to a Compatibility Jamo character."""
-    ...
+    raise NotImplementedError
 
 
 def compat_jaum_to_choseong(c: str, /) -> str | None:
     """Maps a Compatibility Jaum character to a Jamo Choseong character."""
-    ...
+    raise NotImplementedError
 
 
 def compat_moum_to_jungseong(c: str, /) -> str:
     """Maps a Compatibility Moum character to a Jamo Jungseong character."""
-    ...
+    raise NotImplementedError
 
 
 def compat_jaum_to_jongseong(c: str, /) -> str:
     """Maps a Compatibility Jaum character to a Jamo Jongseong character."""
-    ...
+    raise NotImplementedError