MIL-005: Step 4 - Save progress

Review record RC-027 (Go, autonomous mode, not independent).

Task: MIL-005#1
Task: MIL-005#2
Task: MIL-005#3
Task: MIL-005#4
Task: MIL-005#5

src/flash_card/infrastructure/persistence/csv_progress_repository.py

@@ -0,0 +1,44 @@
+"""CSV implementation of the progress port.
+
+@file csv_progress_repository.py
+@brief The CsvProgressRepository adapter.
+"""
+
+from pathlib import Path
+
+from flash_card.domain.entities.deck import Deck
+from flash_card.infrastructure.persistence.csv_word_list import (
+    read_word_list,
+    write_word_list,
+)
+
+
+class CsvProgressRepository:
+    """Keeps the words still to learn in a CSV file."""
+
+    def __init__(self, path: Path) -> None:
+        """Create the repository.
+
+        @param path The words to learn file.
+        """
+        ## @brief The words to learn file.
+        self._path = path
+
+    def load(self) -> Deck | None:
+        """Load the saved words to learn.
+
+        @return The deck, possibly empty, or None when the file does not exist.
+        @throws VocabularyFormatError When the file is malformed; it is left as is.
+        """
+        if not self._path.exists():
+            return None
+        pair, cards = read_word_list(self._path)
+        return Deck(pair, cards)
+
+    def save(self, deck: Deck) -> None:
+        """Save the words still to learn.
+
+        @param deck The cards still to learn.
+        @return Nothing.
+        """
+        write_word_list(self._path, deck.language_pair, deck.cards)