MIL-002 NATO converter: modelling, converter code, tests and Doxygen comments

User story, use case and SSD for "spell a word"; spell_word with
try/except KeyError, generate_phonetic with the retry loop, console and CSV
adapters, 49 pytest tests; MIL-002 and the modelling documents accepted with
review records.

Task: MIL-002#1
Task: MIL-002#2
Task: MIL-002#3
Task: MIL-002#4
Task: MIL-002#5
Task: MIL-002#6

tests/domain/test_spelling.py

@@ -0,0 +1,43 @@
+import pytest
+
+from nato_phonetic_alphabet.adapters.csv_alphabet import load_nato_dict
+from nato_phonetic_alphabet.domain.spelling import InvalidWordError, spell_word
+
+ALPHABET = load_nato_dict()
+LETTERS = "ABCDEFGHIJKLMNOPQRSTUVWXYZ"
+
+
+@pytest.mark.parametrize("letter", list(LETTERS))
+def test_spell_word_maps_letter_to_its_code_word(letter: str) -> None:
+    assert spell_word(letter, ALPHABET) == [ALPHABET[letter]]
+
+
+def test_spell_word_uses_known_code_words() -> None:
+    assert spell_word("ADZ", ALPHABET) == ["Alfa", "Delta", "Zulu"]
+
+
+def test_spell_word_covers_all_26_letters() -> None:
+    assert len(spell_word(LETTERS, ALPHABET)) == len(LETTERS)
+
+
+def test_spell_word_is_case_insensitive_for_mixed_case() -> None:
+    assert spell_word("Hello", ALPHABET) == [
+        "Hotel",
+        "Echo",
+        "Lima",
+        "Lima",
+        "Oscar",
+    ]
+
+
+@pytest.mark.parametrize("word", ["a1", "two words", "hi!", "", "ß", "æ"])
+def test_spell_word_raises_for_non_letter_or_empty(word: str) -> None:
+    with pytest.raises(InvalidWordError):
+        spell_word(word, ALPHABET)
+
+
+def test_spell_word_keeps_cause_of_invalid_character() -> None:
+    with pytest.raises(InvalidWordError) as info:
+        spell_word("a1", ALPHABET)
+
+    assert isinstance(info.value.__cause__, KeyError)