fix(coords): Chunk-Namen korrekt für Float-Indizes und Newlines

- chunk_name: Reject float/bool indices like JavaScript (Number.isInteger)
- parse_chunk_name: Use fullmatch instead of match($) to reject strings with trailing newlines
- Add invalidIndices fixture cases to catch these edge cases in both languages

Co-Authored-By: Claude Haiku 4.5 <noreply@anthropic.com>

tests/fixtures/chunk-names.json

@@ -1,5 +1,6 @@
 {
   "pairs": [["A1", 0, 0], ["L1", 11, 0], ["A12", 0, 11], ["L12", 11, 11], ["C10", 2, 9]],
   "lowercase": [["c10", 2, 9], ["l12", 11, 11]],
-  "invalid": ["M1", "A0", "A13", "A", "10", "", "A01", "B-3", " "]
+  "invalid": ["M1", "A0", "A13", "A", "10", "", "A01", "B-3", " ", "A1\n"],
+  "invalidIndices": [[1.5, 3], [3, 2.5], [true, 0], [0, false]]
 }