Fix container-event event_instance_id mismatch between stats_aggregator_fact and event_instance_fact

[tombonfert]

Problem

For a CONTAINER_EVENT, stats_aggregator_fact produced a different event_instance_id
than event_instance_fact for the same event.

Cause

StatsAggregator._add_event_instance_id_column called generate_event_instance_id_column
without an event type, so container-event rows used the timestamp-based hash
(crc32(container_id::event_name::start_ts::end_ts)) instead of crc32(container_id).
Since timestamps vary per aggregation, the id fragmented.

Fix

Apply the ContainerEvent case per row (keyed on stats_name, like the sibling
mappers), routing through generate_event_instance_id_column(event_type=ContainerEvent)
so the id matches event_instance_fact by construction.

Tests

• New regression test for container-event + stats id consistency (fails without the fix).
• Tightened test_persist_statistics_with_events, whose old assertion always passed.
• Full stats/container-event sweep green; lint clean.

Test Plan

• Unit tests added/updated
• Manual testing completed
• Documentation updated (if applicable)

Checklist

• Code follows project style guidelines
• Self-review completed
• No new linter warnings introduced

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 89.01%. Comparing base (a042e3c) to head (0dd027c).

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #83      +/-   ##
==========================================
+ Coverage   88.99%   89.01%   +0.01%     
==========================================
  Files          61       61              
  Lines        5199     5207       +8     
  Branches      627      628       +1     
==========================================
+ Hits         4627     4635       +8     
  Misses        461      461              
  Partials      111      111              

Flag	Coverage Δ
query_engine	84.77% <ø> (ø)
reporting	94.24% <100.00%> (+0.01%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Files with missing lines	Coverage Δ
...e_reporting/aggregations/point_value_aggregator.py	97.64% <ø> (ø)
...impulse_reporting/aggregations/stats_aggregator.py	94.25% <100.00%> (+0.22%)	⬆️

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