refactor: fix unused imports, long lines, and type issues

Remove 35+ unused imports across 20+ files (W0611). Wrap 19 lines
to fit under 100 character limit (C0301). Add type casts and
annotations in egress_addon_core.py to resolve pyright errors
caused by JSON parsing of untyped objects.

Key changes:
- Remove unused imports (abstractmethod, mock utilities, etc)
- Split long lines at logical breaks (method calls, error messages)
- Add typing.cast() for proper type inference in JSON parsing
- Explicit type annotations for dict/list accesses

Results:
- Pylint rating: 8.73/10
- egress_addon_core.py: 0 pyright errors (was 15)
- All W0611 and C0301 issues fixed

Co-Authored-By: Claude Haiku 4.5 <noreply@anthropic.com>

bot_bottle/manifest.py

@@ -57,7 +57,6 @@ from .manifest_egress import (
     EgressConfig,
     EgressRoute,
     PipelockRoutePolicy,
-    validate_egress_routes,
 )
 from .manifest_git import GitEntry, GitUser, parse_git_gate_config
 from .manifest_schema import BOTTLE_KEYS
@@ -323,8 +322,11 @@ class Manifest:
             return
         available = ", ".join(self.agents.keys())
         if available:
-            raise ManifestError(f"agent '{name}' not defined in bot-bottle.json. Available: {available}")
-        raise ManifestError(f"agent '{name}' not defined in bot-bottle.json (manifest is empty).")
+            msg = f"agent '{name}' not defined in bot-bottle.json. Available: {available}"
+            raise ManifestError(msg)
+        raise ManifestError(
+            f"agent '{name}' not defined in bot-bottle.json (manifest is empty)."
+        )
 
     def has_bottle(self, name: str) -> bool:
         return name in self.bottles