feat: add proper optional-dependencies for each modules (#75)

src/fastapi_toolsets/metrics/__init__.py

@@ -1,8 +1,19 @@
 """Prometheus metrics integration for FastAPI applications."""
 
-from .handler import init_metrics
+from typing import Any
+
 from .registry import Metric, MetricsRegistry
 
+try:
+    from .handler import init_metrics
+except ImportError:
+
+    def init_metrics(*_args: Any, **_kwargs: Any) -> None:
+        from .._imports import require_extra
+
+        require_extra(package="prometheus_client", extra="metrics")
+
+
 __all__ = [
     "Metric",
     "MetricsRegistry",