Cover edge padding CLI aliases

[Spiffical]

What changed

• rename the negative padding test to describe both edge-padding aliases
• exercise --clip-pad-seconds and --edge-pad-seconds with and without event mode
• give each parametrized mode a readable test ID

Why

The previous test name only mentioned clip padding and only covered the non-event path, making failures less informative and leaving event-mode behavior without direct regression coverage.

User impact

No runtime behavior changes. The expanded regression matrix protects clean argparse errors for both aliases in every relevant mode.

Validation

• 7 passed in the focused CLI suite
• 68 passed, 2 deselected in the full offline suite
• git diff --check

[Copilot]

Pull request overview

This PR expands regression coverage for the generate_spectrograms.py CLI to ensure both edge-padding aliases (--clip-pad-seconds and --edge-pad-seconds) produce clean argparse-style errors (no traceback) for negative values in both event and non-event modes.

Changes:

• Renames the negative padding test to reflect both edge-padding aliases.
• Adds event-mode and non-event-mode coverage for each alias via parametrization.
• Improves parametrized-case readability by adding explicit test IDs for event-mode variants.

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