fix: query stats always logs zero value(#11264)

[littlepangdi]

What this PR does / why we need it:
Populates the querier stats with data derived from the query range response stats. This change allows the frontend component to access and log stats information passed through the context, providing a more comprehensive view of query performance.

Which issue(s) this PR fixes:
Fixes #11264 , fix zero value in "query stats" logs.

Since querier_stats.Stats is set to context here but never updated before log，we'll always get zero values in logs.
The code referenced in the issue #11264 is very clear, so I will not repeat it here.

Before fixing:

once -frontend.query-stats-enabled option is enabled, followed logs will be printed. query_wall_time_seconds,fetched_series_count,fetched_series_count always report 0

level=info ts=2025-09-25T08:02:18.065274Z caller=handler.go:323 org_id=xxx msg="query stats" component=query-frontend method=GET status=200 path=/loki/api/v1/query_range response_time=1.574975625s **query_wall_time_seconds=0 fetched_series_count=0 fetched_chunks_bytes=0** param_direction=backward param_query="{app_name=\"hlth-async-handler\"}" param_limit=1 param_start=1758542240865000000 param_end=1758545840865000000 header_x_grafana_user=huxiang header_user_agent=Grafana/8.5

After this fixing:

query_wall_time_seconds,fetched_series_count,fetched_series_count will be accurate values as result.stats.

level=info ts=2025-09-25T07:47:56.16836Z caller=handler.go:323 org_id=xxx msg="query stats" component=query-frontend method=GET status=200 path=/loki/api/v1/query_range response_time=789.782583ms query_wall_time_seconds=0.959356417 fetched_series_count=5052 fetched_chunks_bytes=762099 param_start=1758542240865000000 param_end=1758545840865000000 param_direction=backward param_query="xxx" param_limit=1 header_x_grafana_user=huxiang header_user_agent=Grafana/8.5

Special notes for your reviewer:

Checklist

• Reviewed the CONTRIBUTING.md guide (required)
• Documentation added
• Tests updated
• Title matches the required conventional commits format, see here
  • Note that Promtail is considered to be feature complete, and future development for logs collection will be in Grafana Alloy. As such, feat PRs are unlikely to be accepted unless a case can be made for the feature actually being a bug fix to existing behavior.
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