Add automated SPARQL syntax validation for all queries

[Copilot]

Adds comprehensive SPARQL linting to catch syntax errors before merge. All 49 SPARQL files across queries/ and ical/ directories are now automatically validated.

Implementation

• Test suite (tests/test_lint_all_sparql_files.py): Parametrized pytest that discovers and validates all .sparql files using rdflib.plugins.sparql.prepareQuery

• GitHub workflow (.github/workflows/test-sparql.yml): Runs on PRs and pushes to main when SPARQL files, tests, or dependencies change

Edge cases handled

• Federated SERVICE calls: Replaced with stub VALUES clauses since rdflib can't parse without network
• Vendor-specific syntax: Strips from onto:explicit clause
• RDF-star syntax: 3 files use quoted triples (<< ?s ?p ?o >>) not supported by rdflib - validated structurally via regex, skipped full parse

Validation results

• 46 files: Full syntax validation via rdflib parser
• 3 files: Basic structural validation (SELECT/CONSTRUCT/WHERE clauses present)

Original prompt

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This section details on the original issue you should resolve

<issue_title>Lint all SPARQLs</issue_title>
<issue_description>Modify the Python tests to lint all the SPARQL files in the query directory and in the iCal directory. Add a workflow that runs this test before a commit can be merged with the main branch. </issue_description>

<agent_instructions>Only use Python tests not Ruby tests.</agent_instructions>

Comments on the Issue (you are @copilot in this section)

• Fixes Lint all SPARQLs #29

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[saumier]

Since Python libraries do not support Triple terms (<< >>) then I don't think this will be a good approach since I am adding more use of triple terms to the SPARQLs to track provenance.