Setter for block_sizes and a new method for getting a reduced representation of the sparse object

[awinka]

Added setter for block_sizes, which is used in the screened interaction calculation of quatrex when going to larger block_sizes.

Another method is also added for the calculation of the GW self-energy. Because the buffer for W is larger than that for G, we have to reduce W to the same sparsity pattern as G. This is handled by the calc_reduce_to_mask and reduce_to methods.

[codecov-commenter]

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Codecov Report

Attention: Patch coverage is 87.93103% with 7 lines in your changes missing coverage. Please review.

Project coverage is 84.63%. Comparing base (58c7c3e) to head (9cf8737).

Files with missing lines	Patch %	Lines
src/qttools/datastructures/dsbcoo.py	82.35%	3 Missing :warning:
src/qttools/datastructures/dsbsparse.py	88.46%	3 Missing :warning:
src/qttools/datastructures/dsbcsr.py	93.33%	1 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## awinka/dirty_matmul #55 +/- ## ======================================================= + Coverage 84.48% 84.63% +0.15% ======================================================= Files 29 29 Lines 1160 1217 +57 ======================================================= + Hits 980 1030 +50 - Misses 180 187 +7 ```

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[vetschn]

I'll merge this into the matmul branch and do a review of both things there :)