feat: add HIF format support for hypergraph export and import

[yuxizhe]

No description provided.

[Copilot]

Pull Request Overview

This PR adds support for HIF (Hypergraph Interchange Format) import/export functionality to the HypergraphDB class, enabling standardized data exchange with other hypergraph tools.

• Implements to_hif(), save_as_hif(), from_hif(), and load_from_hif() methods for HIF format support
• Adds comprehensive test coverage for HIF export/import, roundtrip conversion, and attribute preservation
• Updates documentation in README and API docs to describe the new HIF functionality

Reviewed Changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
hyperdb/hypergraph.py	Adds HIF format export/import methods with incidence-based format handling
tests/test_hypergraph.py	Adds three test functions covering HIF export/import, roundtrip, and attribute preservation
docs/api/index.md	Documents new HIF-related methods in persistence operations table
docs/api/index.zh.md	Chinese documentation for HIF functionality with usage examples
README.md	Adds HIF format save/load examples to the persistence section

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[Copilot]

String-based edge matching is fragile and could produce false positives. For example, edge IDs '10_11' and '21_22' would both match when looking for edges containing '1' and '2'. Use exact comparison instead: if e['edge'] == '1_2' or set(str(e['edge']).split('_')) == {'1', '2'}.

Suggested change

	(e for e in hif_data["edges"] if "1" in str(e["edge"]) and "2" in str(e["edge"])),
	(
	e
	for e in hif_data["edges"]
	if (
	(isinstance(e["edge"], (tuple, list)) and set(e["edge"]) == {1, 2})
	or
	(isinstance(e["edge"], str) and set(e["edge"].split("_")) == {"1", "2"})
	)
	),

[Copilot]

This assignment to 'e_attrs' is unnecessary as it is redefined before this value is used.

Suggested change

e_attrs = {k: v for k, v in e_data.items() if k != "weight"}