refactor!: remove deprecated StatisticsState.crawler_runtime setter (#2315)

Removes the `StatisticsState.crawler_runtime` setter. The runtime is
computed from the start and finish timestamps, so the setter only warned
and threw the value away. Assigning to the property now raises
`AttributeError`. The v2 upgrade guide has a short note about it.

Closes: #1567

*✍️ Drafted by Claude Code*

Author: vdusek

docs/06_upgrading/upgrading_to_v2.md

@@ -12,3 +12,7 @@ We drop support for Python 3.10, which reached its end of life in October 2026.
 ## `Event` is a `StrEnum`
 
 `Event` now subclasses `enum.StrEnum`. Calling `str()` on a member or formatting it in an f-string returns its value, for example `'systemInfo'`, where v1 returned `'Event.SYSTEM_INFO'`. Comparisons with plain strings work the same way as in v1.
+
+## `StatisticsState.crawler_runtime` is read-only
+
+`StatisticsState.crawler_runtime` is computed from the crawler's start and finish timestamps. In v1, assigning to it only emitted a `DeprecationWarning` and the value was ignored. In v2, the property has no setter, so an assignment raises `AttributeError`. Remove any such assignments.

src/crawlee/statistics/_models.py

@@ -1,7 +1,6 @@
 from __future__ import annotations
 
 import json
-import warnings
 from dataclasses import asdict, dataclass
 from datetime import UTC, datetime, timedelta
 from typing import TYPE_CHECKING, Annotated, Any
@@ -117,17 +116,6 @@ def crawler_runtime(self) -> timedelta:
             return self._runtime_offset + finished_at - self.crawler_last_started_at
         return self._runtime_offset
 
-    @crawler_runtime.setter
-    def crawler_runtime(self, value: timedelta) -> None:
-        # Setter for backwards compatibility only, the crawler_runtime is now computed_field, and can't be set manually.
-        # To be removed in v2 release https://github.com/apify/crawlee-python/issues/1567
-        warnings.warn(
-            f"Setting 'crawler_runtime' is deprecated and will be removed in a future version."
-            f' Value {value} will not be used.',
-            DeprecationWarning,
-            stacklevel=2,
-        )
-
     @computed_field(alias='crawlerRuntimeMillis')
     def crawler_runtime_for_serialization(self) -> timedelta:
         if self.crawler_last_started_at: