Improve performance of ToSparseMatrix by reducing memory allocations

[robomics]

No description provided.

[codecov]

Codecov Report

Attention: Patch coverage is 82.19895% with 34 lines in your changes missing coverage. Please review.

Project coverage is 79.08%. Comparing base (0dafc0d) to head (e5cd665).
Report is 22 commits behind head on main.

Files with missing lines	Patch %	Lines
.../hictk/transformers/impl/to_sparse_matrix_impl.hpp	80.89%	4 Missing and 26 partials ⚠️
...transformers/include/hictk/transformers/common.hpp	89.47%	1 Missing and 1 partial ⚠️
...e/hictk/transformers/impl/to_dense_matrix_impl.hpp	86.66%	1 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #277      +/-   ##
==========================================
+ Coverage   79.02%   79.08%   +0.06%     
==========================================
  Files         171      171              
  Lines       16324    16479     +155     
  Branches     2250     2278      +28     
==========================================
+ Hits        12900    13033     +133     
+ Misses       2455     2452       -3     
- Partials      969      994      +25     

Flag	Coverage Δ
[tests	integration](https://app.codecov.io/gh/paulsengroup/hictk/pull/277/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=paulsengroup)	69.55% <ø> (+0.12%)
[tests	unittests](https://app.codecov.io/gh/paulsengroup/hictk/pull/277/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=paulsengroup)	76.54% <82.19%> (+0.10%)

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