style: apply ruff's automatic fixes and formatter

Mechanical only, and separated from the judgment calls that follow so the
reviewable changes are not buried in a 98-file whitespace diff.

227 automatic fixes: 60 blank lines carrying whitespace, 60 unsorted import
blocks, 34 Optional[X] to X | None, 28 unused imports, 16 deprecated typing
imports, 12 datetime.timezone.utc to datetime.UTC, and assorted smaller
modernisations. Then `ruff format` over src and tests: 98 files reformatted,
35 already conforming.

No file among the unused-import findings defines __all__ or is an __init__.py,
so nothing here removes a re-export.

`make test`: 658 passed, unchanged from HEAD.

Two things observed while verifying, neither addressed here:

`pytest tests/` cannot collect — tests/e2e/test_orchestration_e2e.py uses an
`e2e` marker that is not registered, and the config is strict about markers.
This fails identically at HEAD, so it predates this change; `make test` passes
because it ignores tests/e2e, tests/integration and tests/contracts.

test_tatlock_tool_call_logging_calculator is flaky. It failed once in a full run
with these changes and passed on the next, passes in isolation with them, and
fails in isolation at HEAD. It is order- or timing-dependent, not a regression
from this commit — established by running the full suite both ways rather than
by reasoning about which change could have caused it.

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

tests/core/test_logging_config.py

@@ -3,12 +3,11 @@ Tests for structured logging configuration.
 
 Tests logging setup, context management, and FastAPI integration.
 """
+
 import logging
-from io import StringIO
 from unittest.mock import patch
 
 import pytest
-import structlog
 
 from src.core.logging_config import (
     add_log_level,
@@ -50,10 +49,10 @@ class TestGetLogger:
         """Test get_logger returns structlog BoundLogger."""
         logger = get_logger("test")
         # Logger should have standard logging methods
-        assert hasattr(logger, 'info')
-        assert hasattr(logger, 'debug')
-        assert hasattr(logger, 'warning')
-        assert hasattr(logger, 'error')
+        assert hasattr(logger, "info")
+        assert hasattr(logger, "debug")
+        assert hasattr(logger, "warning")
+        assert hasattr(logger, "error")
 
     def test_get_logger_with_module_name(self):
         """Test logger with module name."""