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

pyproject.toml

@@ -54,7 +54,7 @@ dependencies = [
     "urllib3>=2.2.1,<3",
     "chardet>=5.2.0,<6",
     "curl-cffi>=0.7.0b4,<0.8",
-    "pyplayready>=0.6.0,<0.7",
+    "pyplayready>=0.6.3,<0.7",
     "httpx>=0.28.1,<0.29",
     "cryptography>=45.0.0",
     "subby",
@@ -113,4 +113,4 @@ no_implicit_optional = true
 
 [tool.uv.sources]
 unshackle = { workspace = true }
-subby = { git = "https://github.com/vevv/subby.git" }
+subby = { git = "https://github.com/vevv/subby.git", rev = "5a925c367ffb3f5e53fd114ae222d3be1fdff35d" }