Complete Overhaul of the Statistics Module

## Problem
Currently, the statistics code resides in a raw, unconfigured project within a private repository. Moreover, more than half of the code is a direct copy of an old version of statistics from Lets-Plot (core), without incorporating any of the fixes made in Lets-Plot. Every time we need add a new statistics we must copy-paste Lets-Plot code again. Additionally, the statistics module completely lacks tests.

Furthermore, statistics are published as a separate artifact, which frequently causes integration issues for users.

## Tasks
- Align the codebase with Lets-Plot to avoid duplication and inconsistencies (simplest solution - use LP internal statistics API for implementation).
- Move the Statistics API to the main repository.
- Possibly integrate it into `kandy-lets-plot`, eliminating the need for a separate artifact, as it serves no real purpose.
- Then, we can add API for remaining statistics and statistical plots (#369).

This also will fix #276.

Start by mapping the current Statistics API and its separate artifact, then compare the implementation with Lets-Plot's internal statistics API. Evaluate whether kandy-lets-plot is the intended integration point, and define completion as an aligned, unified statistics module with tests and a path for adding the remaining statistics and statistical plots.

Written by the indexing model from the issue text.