fix(parse): register a filing's packages for that load only

[jfrench9]

Summary

Arelle keeps registered taxonomy packages for the life of the process, and xbrlkit never cleared them. In a long-running session (the MCP server) a load could therefore resolve through an earlier load's catalog. load_model now clears the registrations before each load, so a filing resolves through its own packages and no one else's.

Changes

parse/ (convert)

• _register_packages calls PackageManager.reset() before registering the packages for the load, and when there are none.
• parse/README.md says a package is registered for the one load.

Tests

• Two new tests in tests/test_arelle_cache.py drive real Arelle, offline with a cold cache, over small synthetic packages. Both fail without the change.

Output Impact

INTERNAL for a filing loaded in a fresh process: its output is unchanged.

For a process that loads more than one filing, three wrong results go away. Each was reproduced on 0.20.7 with real Arelle:

• A report with no package, loaded after a package that maps the URL it cites, read that package's taxonomy and loaded. In a fresh process it is refused with the URL unresolved, and now it is refused in both.
• The same report, after the earlier filing had been unloaded and its files removed, loaded with no facts and no error. It is now refused.
• Of two packages with different identifiers that map the same URL to different schemas, the first, loaded again after the second, was read through the second's schema and came back with no facts. It now reads its own.

Two versions of one real filing that share a package identifier were not affected before the change, in any load order, and are not affected after it.

Testing

• The pre-commit hook ran ruff check, ruff format, basedpyright and the suite on the commit: 685 passed, 2 skipped.
• The three cases above were run on synthetic packages before and after the change.
• Real filings, one process, after the change: nine loads from filings.xbrl.org in sequence — a .xbri package (7245003GZ2696Y0W1X57-2026-03-31-ESEF-NL-0), a Danish report (549300DAQ1CVT6CXN342-2026-06-30-ESEF-DK-0), a backslash-zipped package (743700G7A9J1PHM3X223-2020-12-31-ESEF-FI-1), three ordinary ESEF packages, and a two-version pair of one filing loaded first, second, first. Fact counts match the same filings loaded in isolated processes.
• An SEC 10-Q (NVDA 10-Q, parsed from EDGAR with the CDN turned off) loaded between two loads of the same ESEF package; the package's model was identical before and after.

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