fix: preserve integer indices in empty SparseEmbedding.from_dict results

[RAMZI0TO99]

SparseEmbedding.from_dict({}) currently creates float64 indices, so even assigning empty values with dense[embedding.indices] = embedding.values raises NumPy's integer-index error. This sets the empty indices to int64, preserving valid NumPy indexing and integer concatenation.

The nonempty conversion and values array are unchanged. Regression tests cover empty arrays/indexing, pairing and dictionary round trips, concatenation, and empty BM25 document embeddings.

Validation on Windows 11, Python 3.13.5, NumPy 2.3.5, FastEmbed 0.8.1:

• 14 selected tests passed: python -m pytest -q tests/test_sparse_embedding_base.py tests/test_common.py.
• Local diff-scoped AST docstring coverage: 5/5 functions (100%, above the reported 80% threshold). CodeRabbit's own result is separate.
• Ruff 0.3.4 lint/format and staged whitespace checks passed.
• Repository mypy and pyright checks passed on Python 3.13.5.

The full model/OS/Python CI matrix was not run locally.

Split from #766 following the maintainer's request for one PR per problem. This branch is based directly on current main and contains only this problem's production change and regression module.

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Reviewing files that changed from the base of the PR and between 58264f7 and c84db45.

📒 Files selected for processing (2)

• fastembed/sparse/sparse_embedding_base.py
• tests/test_sparse_embedding_base.py

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📝 Walkthrough

Walkthrough

SparseEmbedding.from_dict now returns int64 indices for empty mappings and documents that mapping iteration order is retained. Regression tests cover empty and unsorted mappings, concatenation of empty and nonempty embeddings, and BM25 documents whose tokens are all removed.

Priority: ⬇️ Low

Estimated code review effort: 2 (Simple) | ~10 minutes

Change: Bug fix

Merge Risk: ⚪ Minimal · up to c84db

The empty sparse-embedding indexing fix is ready to merge after normal checks.

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly identifies the fix: preserving integer indices for empty SparseEmbedding.from_dict results.
Description check	✅ Passed	The description explains the empty-index bug, the change, regression tests, and validation results.
Docstring Coverage	✅ Passed	Docstring coverage is 100.00% which is sufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 5 functions across 2 files.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

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[joein]

thanks for the fix!