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>

src/core/logging_config.py

@@ -4,12 +4,14 @@ Structured logging configuration using structlog.
 Deeply integrates with FastAPI/uvicorn's built-in logging to provide
 seamless structured logs across the entire application stack.
 """
+
 import logging
 import logging.config
 import sys
+from collections.abc import AsyncIterator
 from contextlib import asynccontextmanager
-from datetime import datetime, timezone
-from typing import Any, AsyncIterator
+from datetime import UTC, datetime
+from typing import Any
 
 import structlog
 from structlog.types import EventDict, Processor
@@ -19,7 +21,7 @@ from .config import config
 
 def add_timestamp(logger: Any, method_name: str, event_dict: EventDict) -> EventDict:
     """Add ISO 8601 timestamp to log entries."""
-    event_dict["timestamp"] = datetime.now(timezone.utc).isoformat()
+    event_dict["timestamp"] = datetime.now(UTC).isoformat()
     return event_dict
 
 
@@ -41,11 +43,28 @@ def extract_from_record(logger: Any, method_name: str, event_dict: EventDict) ->
         # Extract custom fields from record
         for key, value in record.__dict__.items():
             if key not in {
-                "name", "msg", "args", "created", "filename", "funcName",
-                "levelname", "levelno", "lineno", "module", "msecs",
-                "message", "pathname", "process", "processName", "relativeCreated",
-                "thread", "threadName", "exc_info", "exc_text", "stack_info",
-                "taskName"
+                "name",
+                "msg",
+                "args",
+                "created",
+                "filename",
+                "funcName",
+                "levelname",
+                "levelno",
+                "lineno",
+                "module",
+                "msecs",
+                "message",
+                "pathname",
+                "process",
+                "processName",
+                "relativeCreated",
+                "thread",
+                "threadName",
+                "exc_info",
+                "exc_text",
+                "stack_info",
+                "taskName",
             }:
                 event_dict[key] = value
 
@@ -164,7 +183,7 @@ def get_logger(name: str) -> structlog.stdlib.BoundLogger:
 async def log_operation(
     operation: str,
     initial_context: dict[str, Any] | None = None,
-    logger_name: str = "tatlock.operations"
+    logger_name: str = "tatlock.operations",
 ) -> AsyncIterator[dict[str, Any]]:
     """
     Context manager for automatic operation timing and logging.
@@ -187,21 +206,21 @@ async def log_operation(
     context = initial_context or {}
     context["operation"] = operation
 
-    start_time = datetime.now(timezone.utc)
+    start_time = datetime.now(UTC)
     logger.info("operation_started", **context)
 
     try:
         yield context
 
         # Success case
-        duration = (datetime.now(timezone.utc) - start_time).total_seconds()
+        duration = (datetime.now(UTC) - start_time).total_seconds()
         context["duration_seconds"] = duration
         context["success"] = True
         logger.info("operation_completed", **context)
 
     except Exception as e:
         # Error case
-        duration = (datetime.now(timezone.utc) - start_time).total_seconds()
+        duration = (datetime.now(UTC) - start_time).total_seconds()
         context["duration_seconds"] = duration
         context["success"] = False
         context["error"] = str(e)
@@ -228,7 +247,8 @@ def get_uvicorn_log_config() -> dict[str, Any]:
                 "()": structlog.stdlib.ProcessorFormatter,
                 "processors": [
                     structlog.stdlib.ProcessorFormatter.remove_processors_meta,
-                    structlog.processors.JSONRenderer() if config.log_format == "json"
+                    structlog.processors.JSONRenderer()
+                    if config.log_format == "json"
                     else structlog.dev.ConsoleRenderer(colors=True),
                 ],
             },