Extend arithmetic operator support for accumulators

[HDembinski]

All accumulators support addition and scaling (multiplication by a constant). Additionally, we could support subtraction, multiplication, and division.

Subtraction

• [ ] count
• [ ] sum
• [ ] weighted_sum
• [ ] mean
• [ ] weighted_mean

Multiplication

• [ ] count
• [ ] sum
• [ ] weighted_sum
• [ ] mean
• [ ] weighted_mean

Division

• [ ] count
• [ ] sum
• [x] weighted_sum
• [ ] mean
• [ ] weighted_mean

How to implement division and multiplication for weighted mean is mathematically not clear to me.