GraphRAG: Better search for entities

[javitonino]

Moves the logic to search for entities from graph strategy to nidx, so it can be done faster and in a single index request.

[codecov]

Codecov Report

Attention: Patch coverage is 90.00000% with 1 line in your changes missing coverage. Please review.

Project coverage is 86.76%. Comparing base (c09e5c2) to head (586805f).
Report is 8 commits behind head on main.

Files with missing lines	Patch %	Lines
...liadb/src/nucliadb/search/search/graph_strategy.py	80.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2834      +/-   ##
==========================================
- Coverage   86.87%   86.76%   -0.11%     
==========================================
  Files         380      380              
  Lines       23879    23868      -11     
==========================================
- Hits        20744    20710      -34     
- Misses       3135     3158      +23     

Flag	Coverage Δ
nucliadb	75.22% <90.00%> (-0.14%)	⬇️
nucliadb-ingest	40.98% <20.00%> (+<0.01%)	⬆️
nucliadb-reader	42.72% <20.00%> (-0.01%)	⬇️
nucliadb-search	44.18% <20.00%> (+0.01%)	⬆️
nucliadb-standalone	47.36% <20.00%> (+0.01%)	⬆️
nucliadb-train	45.51% <20.00%> (+0.01%)	⬆️
nucliadb-writer	46.81% <20.00%> (+0.01%)	⬆️
nucliadb_dataset	55.45% <ø> (ø)
nucliadb_models	85.62% <ø> (-0.16%)	⬇️
nucliadb_sdk	83.13% <ø> (ø)
nucliadb_telemetry	86.56% <ø> (ø)
nucliadb_utils	83.79% <ø> (ø)

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