Update diagnostics

[ahartikainen]

Description

Let's update our diagnostics to be synced with R posterior package.

https://github.com/stan-dev/posterior/blob/master/R/convergence.R

This means, we need to

• fix off-by-one error in mcse_quantile.
• update rankdata transformation

Checklist

• Follows official PR format
• Includes a sample plot to visually illustrate the changes (only for plot-related functions)
• New features are properly documented (with an example if appropriate)?
• Includes new or updated tests to cover the new feature
• Code style correct (follows pylint and black guidelines)
• Changes are listed in changelog

[ahartikainen]

The difference after the change is minimal

(normal random data N=100 --> 4.9515613831374594e-11)

[ahartikainen]

I will update the reference diagnostics to use posterior package.

[codecov]

Codecov Report

Merging #1366 into master will decrease coverage by 0.00%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master    #1366      +/-   ##
==========================================
- Coverage   91.74%   91.73%   -0.01%     
==========================================
  Files         102      102              
  Lines       10778    10771       -7     
==========================================
- Hits         9888     9881       -7     
  Misses        890      890              

Impacted Files	Coverage Δ
arviz/stats/stats_utils.py	95.54% <ø> (-0.05%)	⬇️
arviz/stats/diagnostics.py	99.26% <100.00%> (-0.01%)	⬇️

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[canyon289]

Very detailed