Summary

Fix avg_time_weighted incorrect results for signed integer values (issue #1121).

• For _time_weighted + avg, instantiate nested avg_weighted with Float64 weights.
• Keep median_time_weighted unchanged (UInt64 weight path).
• In AggregateFunctionTimeWeighted, support nested weight columns of both UInt64 and Float64.

Root Cause

avg_time_weighted(Int*, time) previously used nested avg_weighted<Value, UInt64>, which could trigger unsigned-promotion/overflow behavior for negative signed inputs.

Compatibility

This PR intentionally does not preserve backward compatibility for previously serialized avg_time_weightedState binary format.
Robust correctness for new computations/merges is prioritized for this fix.

Please write user-readable short description of the changes:
fix #1121