2/3 Resolve mypy type checking issues

Testing done:

```
poetry run mypy src/pygptcourse
Success: no issues found in 4 source files
```

Addresses #29

Based on ChatGPT analysis this is the second commit that addresses
linting issues. This has only the fixes required for mypy.

src/pygptcourse/main.py

@@ -2,7 +2,7 @@
 
 import cv2
 
-import face_recognition
+import face_recognition # type: ignore
 
 from pygptcourse.tshirt_launcher import Launcher
 from pygptcourse.tshirt_launcher import RIGHT, LEFT, STOP, FIRE, DOWN, UP

src/pygptcourse/tracker.py

@@ -1,5 +1,5 @@
 import cv2
-import face_recognition
+import face_recognition # type: ignore
 
 # Set the total time for moving from left to right and top to bottom
 TOTAL_TIME_LR = 26

src/pygptcourse/tshirt_launcher.py

@@ -4,8 +4,8 @@
 import time
 import threading
 
-import usb.core
-import usb.util
+import usb.core # type: ignore
+import usb.util # type: ignore
 
 VENDOR = 0x1941
 PRODUCT = 0x8021
@@ -212,8 +212,8 @@ def close(self):
         try:
             s = input('{}>> '.format(prompt)).strip()
             print(f"Received command {s}")
-            cmd, delay = s.split()
-            delay = float(delay)
+            cmd, delay_str = s.split()
+            delay = float(delay_str)
         except EOFError:
             cmd = 'quit'
         except ValueError: