fix: upgrade pyplayready to 0.6.3 and resolve import compatibility issues

- Upgrade pyplayready from >=0.6.0 to >=0.6.3
- Upgrade subby to 0.3.23 (commit 5a925c36) for lxml 6.x compatibility
- Upgrade lxml from 5.4.0 to 6.0.2
- Fix pyplayready exception imports to use root-level imports (compatible with both 0.6.0 and 0.6.3)
- Suppress SyntaxWarning from unmaintained tinycss dependency

The pyplayready package changed its API between versions:
- v0.6.0: exceptions in pyplayready.exceptions module
- v0.6.3: exceptions in pyplayready.misc.exceptions module
Using root-level imports (from pyplayready import ...) works with both versions.

ref #20

unshackle/core/__main__.py

@@ -1,10 +1,14 @@
 import atexit
 import logging
+import warnings
 from pathlib import Path
 
 import click
 import urllib3
 from rich import traceback
+
+# Suppress SyntaxWarning from unmaintained tinycss package (dependency of subby)
+warnings.filterwarnings("ignore", category=SyntaxWarning, module="tinycss")
 from rich.console import Group
 from rich.padding import Padding
 from rich.text import Text