refactor(cost,perf): 成本字段 Float 改 Numeric 并优化多处查询性能

- 数据库所有 cost/price 字段从 Float 改为 Numeric(20,8)，解决浮点精度问题
- API 响应中 Decimal 值统一用 float() 转换确保 JSON 序列化
- 路由中手动 commit 后标记 tx_committed_by_route 防止中间件重复提交
- 多处查询优化：SQL 聚合替代 Python 遍历、load_only/defer 减少字段加载、
  批量 DELETE 替代逐条 ORM 删除、N+1 查询消除、UNION ALL 合并多表日期查询
- 新增 provider_api_keys (provider_id, is_active) 复合索引
- 候选构建热路径 defer 冷字段，钱包扣费合并解析与加锁查询

alembic/versions/20260308_1530_2053ab8ed764_cost_fields_float_to_numeric.py

@@ -0,0 +1,165 @@
+"""cost fields: Float -> Numeric(20,8) + provider_api_keys composite index
+
+Revision ID: 2053ab8ed764
+Revises: 13a4c8f6d9e0
+Create Date: 2026-03-08 15:30:00.000000+00:00
+
+"""
+
+import sqlalchemy as sa
+
+from alembic import op
+
+# revision identifiers, used by Alembic.
+revision = "2053ab8ed764"
+down_revision = "13a4c8f6d9e0"
+branch_labels = None
+depends_on = None
+
+
+# (table_name, column_name, nullable, server_default)
+_COST_COLUMNS: list[tuple[str, str, bool, str | None]] = [
+    # api_keys
+    ("api_keys", "total_cost_usd", True, "0.0"),
+    # usage
+    ("usage", "input_cost_usd", True, "0.0"),
+    ("usage", "output_cost_usd", True, "0.0"),
+    ("usage", "cache_cost_usd", True, "0.0"),
+    ("usage", "cache_creation_cost_usd", True, "0.0"),
+    ("usage", "cache_read_cost_usd", True, "0.0"),
+    ("usage", "request_cost_usd", True, "0.0"),
+    ("usage", "total_cost_usd", True, "0.0"),
+    ("usage", "actual_input_cost_usd", True, "0.0"),
+    ("usage", "actual_output_cost_usd", True, "0.0"),
+    ("usage", "actual_cache_creation_cost_usd", True, "0.0"),
+    ("usage", "actual_cache_read_cost_usd", True, "0.0"),
+    ("usage", "actual_request_cost_usd", True, "0.0"),
+    ("usage", "actual_total_cost_usd", True, "0.0"),
+    ("usage", "rate_multiplier", True, "1.0"),
+    ("usage", "input_price_per_1m", True, None),
+    ("usage", "output_price_per_1m", True, None),
+    ("usage", "cache_creation_price_per_1m", True, None),
+    ("usage", "cache_read_price_per_1m", True, None),
+    ("usage", "price_per_request", True, None),
+    # providers
+    ("providers", "monthly_quota_usd", True, None),
+    ("providers", "monthly_used_usd", True, "0.0"),
+    # global_models
+    ("global_models", "default_price_per_request", True, None),
+    # models
+    ("models", "price_per_request", True, None),
+    # stats_hourly
+    ("stats_hourly", "total_cost", False, "0.0"),
+    ("stats_hourly", "actual_total_cost", False, "0.0"),
+    # stats_hourly_user
+    ("stats_hourly_user", "total_cost", False, "0.0"),
+    # stats_hourly_model
+    ("stats_hourly_model", "total_cost", False, "0.0"),
+    # stats_hourly_provider
+    ("stats_hourly_provider", "total_cost", False, "0.0"),
+    # stats_daily
+    ("stats_daily", "total_cost", False, "0.0"),
+    ("stats_daily", "actual_total_cost", False, "0.0"),
+    ("stats_daily", "input_cost", False, "0.0"),
+    ("stats_daily", "output_cost", False, "0.0"),
+    ("stats_daily", "cache_creation_cost", False, "0.0"),
+    ("stats_daily", "cache_read_cost", False, "0.0"),
+    # stats_daily_model
+    ("stats_daily_model", "total_cost", False, "0.0"),
+    # stats_daily_provider
+    ("stats_daily_provider", "total_cost", False, "0.0"),
+    # stats_daily_api_key
+    ("stats_daily_api_key", "total_cost", False, "0.0"),
+    # stats_summary
+    ("stats_summary", "all_time_cost", False, "0.0"),
+    ("stats_summary", "all_time_actual_cost", False, "0.0"),
+    # stats_user_daily
+    ("stats_user_daily", "total_cost", False, "0.0"),
+]
+
+# rate_multiplier uses a smaller precision
+_RATE_MULTIPLIER_TYPE = sa.Numeric(10, 6)
+_COST_TYPE = sa.Numeric(20, 8)
+
+
+def _column_exists(table_name: str, column_name: str) -> bool:
+    bind = op.get_bind()
+    result = bind.execute(
+        sa.text(
+            "SELECT 1 FROM information_schema.columns "
+            "WHERE table_name = :table AND column_name = :col"
+        ),
+        {"table": table_name, "col": column_name},
+    )
+    return result.scalar() is not None
+
+
+def _index_exists(index_name: str) -> bool:
+    bind = op.get_bind()
+    result = bind.execute(
+        sa.text("SELECT 1 FROM pg_indexes WHERE indexname = :name"),
+        {"name": index_name},
+    )
+    return result.scalar() is not None
+
+
+def _is_numeric_type(table_name: str, column_name: str) -> bool:
+    """Check if a column is already numeric type (not float/double precision)."""
+    bind = op.get_bind()
+    result = bind.execute(
+        sa.text(
+            "SELECT data_type FROM information_schema.columns "
+            "WHERE table_name = :table AND column_name = :col"
+        ),
+        {"table": table_name, "col": column_name},
+    )
+    data_type = result.scalar()
+    return data_type == "numeric"
+
+
+def upgrade() -> None:
+    # -- 1. cost fields: Float -> Numeric
+    for table, col, _nullable, _default in _COST_COLUMNS:
+        if not _column_exists(table, col):
+            continue
+        if _is_numeric_type(table, col):
+            continue
+        target_type = _RATE_MULTIPLIER_TYPE if col == "rate_multiplier" else _COST_TYPE
+        op.alter_column(
+            table,
+            col,
+            type_=target_type,
+            existing_type=sa.Float(),
+            postgresql_using=f"{col}::numeric",
+        )
+
+    # -- 2. provider_api_keys composite index
+    if not _index_exists("idx_provider_api_keys_provider_active"):
+        op.create_index(
+            "idx_provider_api_keys_provider_active",
+            "provider_api_keys",
+            ["provider_id", "is_active"],
+        )
+
+
+def downgrade() -> None:
+    # -- 2. drop composite index
+    if _index_exists("idx_provider_api_keys_provider_active"):
+        op.drop_index(
+            "idx_provider_api_keys_provider_active",
+            table_name="provider_api_keys",
+        )
+
+    # -- 1. Numeric -> Float
+    for table, col, _nullable, _default in _COST_COLUMNS:
+        if not _column_exists(table, col):
+            continue
+        if not _is_numeric_type(table, col):
+            continue
+        op.alter_column(
+            table,
+            col,
+            type_=sa.Float(),
+            existing_type=_COST_TYPE if col != "rate_multiplier" else _RATE_MULTIPLIER_TYPE,
+            postgresql_using=f"{col}::double precision",
+        )