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_git.py

@@ -30,12 +30,18 @@ def parse_git_upstream(url: str, label: str) -> tuple[str, str, str, str]:
         raise ManifestError(f"{label} must be an ssh:// URL (was {url!r})")
     rest = url[len("ssh://"):]
     if "@" not in rest:
-        raise ManifestError(f"{label} must include a user (e.g. ssh://git@host/path.git); was {url!r}")
+        raise ManifestError(
+            f"{label} must include a user (e.g. ssh://git@host/path.git); "
+            f"was {url!r}"
+        )
     user, _, hostpart = rest.partition("@")
     if not user:
         raise ManifestError(f"{label} user is empty in {url!r}")
     if "/" not in hostpart:
-        raise ManifestError(f"{label} must include a path (e.g. ssh://git@host/path.git); was {url!r}")
+        raise ManifestError(
+            f"{label} must include a path (e.g. ssh://git@host/path.git); "
+            f"was {url!r}"
+        )
     hostport, _, path = hostpart.partition("/")
     if not path:
         raise ManifestError(f"{label} path is empty in {url!r}")