Add truncation functionality for SVD

[lkdvos]

This is an initial implementation for truncated SVD for block(permuted)diagonal matrices.
Depends on #111

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 73.27%. Comparing base (6c92d7c) to head (17ccf8e).
Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #113      +/-   ##
==========================================
+ Coverage   72.22%   73.27%   +1.05%     
==========================================
  Files          27       28       +1     
  Lines        1170     1216      +46     
==========================================
+ Hits          845      891      +46     
  Misses        325      325              

Flag	Coverage Δ
docs	12.30% <0.00%> (-0.48%)	⬇️

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[lkdvos]

I added tests and functionality for trunctol as well, success of the tests depends on ITensor/SparseArraysBase.jl#58

I think this should be more or less ready for review, we have to decide how to select truncation strategies and how to make sure the correct blocked ones get selected.