Add Blackjack game: rules, card rendering, game loop and tests

Implement the playable console game for gateway MIL-002.

- rules.py: deal_card, calculate_score (blackjack = 0, aces drop 11 ->
  1)
  and compare with an Outcome enum; no console I/O
- display.py: hand rendering as plain-text rank plus suit emoji (keycap
  emoji rendered as boxes in common terminals), score formatting and
  outcome messages
- art.py: course logo shown at the start of every game
- game.py: play_game (hit/stand, dealer draws below 17), play (restart
  loop, console clear, logo) and ask_yes_no with re-prompt; read, write
  and draw are injected so games can be scripted
- __main__.py: python -m blackjack entry point, exits cleanly on
  Ctrl+C/Ctrl+D
- constants.py: card ranks and suits, prompts and messages
- tests: 32 new unit and scripted end-to-end tests (35 in total)
- README: run instructions for python -m blackjack

Closes #7
Closes #8
Closes #9
Closes #10
Closes #11
Closes #12
Closes #13
Closes #14

Task: MIL-002#1
Task: MIL-002#2
Task: MIL-002#3
Task: MIL-002#4
Task: MIL-002#5
Task: MIL-002#6
Task: MIL-002#7
Task: MIL-002#8

src/blackjack/art.py

@@ -0,0 +1,16 @@
+"""!
+@file art.py
+@brief ASCII art shown at the start of every game.
+"""
+
+## The game logo from the course assignment.
+LOGO: str = r"""
+.------.            _     _            _    _            _
+|A_  _ |.          | |   | |          | |  (_)          | |
+|( \/ ).-----.     | |__ | | __ _  ___| | ___  __ _  ___| | __
+| \  /|K /\  |     | '_ \| |/ _` |/ __| |/ / |/ _` |/ __| |/ /
+|  \/ | /  \ |     | |_) | | (_| | (__|   <| | (_| | (__|   <
+`-----| \  / |     |_.__/|_|\__,_|\___|_|\_\ |\__,_|\___|_|\_\\
+      |  \/ K|                            _/ |
+      `------'                           |__/
+"""