Fix type annotation bugs and remove unused imports

This fixes issues introduced by the ruff commit e57f391a which converted
Optional[x] to x | None:

- Fixed datasette/app.py line 1024: Dict[id | str, Dict] -> Dict[int | str, Dict]
  (was using id built-in function instead of int type)
- Fixed datasette/app.py line 1074: Optional["Resource"] -> "Resource" | None
- Added 'from __future__ import annotations' for Python 3.10 compatibility
- Added TYPE_CHECKING blocks to avoid circular imports
- Removed dead code (unused variable assignments) from cli.py and views
- Removed unused imports flagged by ruff across multiple files
- Fixed test fixtures: moved app_client fixture imports to conftest.py
  (fixed 71 test errors caused by fixtures not being registered)

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

tests/conftest.py

@@ -231,3 +231,27 @@ def ds_unix_domain_socket_server(tmp_path_factory):
     yield ds_proc, uds
     # Shut it down at the end of the pytest session
     ds_proc.terminate()
+
+
+# Import fixtures from fixtures.py to make them available
+from .fixtures import (  # noqa: E402, F401
+    app_client,
+    app_client_base_url_prefix,
+    app_client_conflicting_database_names,
+    app_client_csv_max_mb_one,
+    app_client_immutable_and_inspect_file,
+    app_client_larger_cache_size,
+    app_client_no_files,
+    app_client_returned_rows_matches_page_size,
+    app_client_shorter_time_limit,
+    app_client_two_attached_databases,
+    app_client_two_attached_databases_crossdb_enabled,
+    app_client_two_attached_databases_one_immutable,
+    app_client_with_cors,
+    app_client_with_dot,
+    app_client_with_trace,
+    generate_compound_rows,
+    generate_sortable_rows,
+    make_app_client,
+    TEMP_PLUGIN_SECRET_FILE,
+)