2640 bug lo prostar not processing correctly

[subagonsouth]

Change Summary

Overview

• Fix artifact leftover from misnaming l1b prostar "star".
• Raise when unexpected descriptor gets passed in.
• Fix for issue with L1A files having issue causing dataset to have "shcoarse" dimension that duplicates "epoch".

Closes: #2640

[Copilot]

Pull request overview

This PR fixes two issues with IMAP-Lo prostar (star sensor) L1B processing:

1. Corrects a misnaming issue where the descriptor was "star" instead of "prostar"
2. Fixes a control flow bug where multiple descriptor paths could be executed due to using if statements instead of elif
3. Adds a workaround for L1A files having a shcoarse dimension that duplicates epoch

Changes:

• Changed descriptor from "star" to "prostar" to match the L1B logical source name
• Changed descriptor conditional checks from independent if statements to elif chain to ensure mutual exclusivity
• Added warning logging for unexpected descriptors
• Added temporary fix for shcoarse DEPEND_0 issue in L1A star sensor files
• Added test coverage for unexpected descriptor warning

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
imap_processing/lo/l1b/lo_l1b.py	Updated descriptor handling: changed "star" to "prostar", converted if statements to elif chain, added warning for unexpected descriptors, and added shcoarse dimension workaround
imap_processing/tests/lo/test_lo_l1b.py	Added test to verify warning is logged for unexpected descriptors

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