[leowerneck]

Change Summary

Closes #3579.

Overview

This PR bumps cdflib to version 1.3.15, required to fix #3579, as described in lasp/cdflib#348 and lasp/cdflib#349.

File changes

• pyproject.toml: bumped CDF lib to 1.3.15.
• poetry.lock: bumped CDF lib to 1.3.15.
• imap_processing/tests/cdf/test_utils.py: add regression test.

Testing

Running:

poetry sync --extras test
poetry run pytest -n auto -m "not external_kernel and not external_test_data"

results in 1841 passed tests and no failures.

[Copilot]

🟢 Approval recommended

The upstream release confirms the fix, and the regression test covers both required attribute types with no unresolved findings.

No open issues 🎉

What changed in this PR

Fixes #3579 by adopting the upstream correction for epoch attribute types in generated CDF products.

Changes:

• Raises the minimum and locked cdflib version to 1.3.15.
• Adds regression coverage confirming epoch attributes use TT2000 while epoch-delta attributes remain INT8.

File	Description
pyproject.toml	Requires cdflib>=1.3.15.
poetry.lock	Updates the locked version, package hashes, and content hash.
imap_processing/​tests/​cdf/​test_utils.py	Checks written epoch and epoch-delta attribute types.

_{Review effort: Balanced}