Expand distributed indexing, match numpy indexing scheme

[ClaudiaComito]

Description

DRAFT

Intro: main points from Numpy array indexing scheme

Heat: indexing massive, memory-distributed arrays

process-local indexing

distributed indexing

• sorted key
• non-sorted key

Memory footprint

Scaling behaviour

Issue/s resolved: #914 #918

Changes proposed:

Type of change

Memory requirements

Performance

Due Diligence

• [ ] All split configurations tested
• [ ] Multiple dtypes tested in relevant functions
• [ ] Documentation updated (if needed)
• [ ] Updated changelog.md under the title "Pending Additions"

Does this change modify the behaviour of other functions? If so, which?

yes / no

skip ci

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Legend

[mrfh92]

just a comment: in the fft-module (if already merged at time merging this PR) some commented-out parts of test_rfftn_irfftn can be added again if this PR is ready

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 30.31915% with 131 lines in your changes are missing coverage. Please review.

Project coverage is 66.88%. Comparing base (8ba63c5) to head (5995639).

:exclamation: Current head 5995639 differs from pull request most recent head a8f2d57. Consider uploading reports for the commit a8f2d57 to get more accurate results

Files	Patch %	Lines
heat/core/dndarray.py	26.70%	129 Missing :warning:
heat/core/indexing.py	83.33%	2 Missing :warning:

Additional details and impacted files

@@             Coverage Diff             @@
##             main     #938       +/-   ##
===========================================
- Coverage   91.92%   66.88%   -25.04%     
===========================================
  Files          79       65       -14     
  Lines       11721    10017     -1704     
===========================================
- Hits        10774     6700     -4074     
- Misses        947     3317     +2370     

Flag	Coverage Δ
unit	66.88% <30.31%> (-25.04%)	:arrow_down:

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