Add variables to Hi L1B DE product

[subagonsouth]

Change Summary

Overview

Adds two new variables to the Hi L1B Direct Event product

New Variables

1. esa_step_met (float64, epoch dimension)
   - MET time when the ESA was stepped, computed from esa_step_seconds + esa_step_milliseconds / 1000
   - Provides a convenient floating-point representation of the ESA step timestamp
2. ccsds_qf (uint8, epoch dimension)
   - Quality flag bitmask for each CCSDS packet
   - Bit 0 (PACKET_FULL): Set when packet contains 664 events (maximum capacity)

Implementation Details

• Added de_esa_step_met() function to compute ESA step MET
• Added de_ccsds_qf() function to compute CCSDS quality flags
• Added ImapHiL1bDeFlags flag class to quality_flags.py following existing patterns
• Added variable attribute definitions to imap_hi_variable_attrs.yaml
• L1B DE output now contains 17 data variables (previously 15)

Files Changed

• imap_processing/hi/hi_l1b.py - Added two new processing functions
• imap_processing/quality_flags.py - Added ImapHiL1bDeFlags class
• imap_processing/cdf/config/imap_hi_variable_attrs.yaml - Added variable definitions
• imap_processing/tests/hi/test_hi_l1b.py - Added tests for new functions

Closes: #2746

[Copilot]

Pull request overview

This PR updates the IMAP-Hi L1B Direct Event (DE) product generation to include two new epoch-dimension variables that carry (1) a floating-point ESA step MET timestamp and (2) a CCSDS packet-level quality flag bitmask.

Changes:

• Add esa_step_met derived from esa_step_seconds + esa_step_milliseconds.
• Add ccsds_qf bitmask with PACKET_FULL (bit 0) set for packets containing 664 events.
• Extend variable attribute configuration and add unit tests for the new helpers.

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 2 comments.

File	Description
imap_processing/hi/hi_l1b.py	Adds de_esa_step_met() and de_ccsds_qf() and injects their outputs into the L1B DE dataset.
imap_processing/quality_flags.py	Introduces ImapHiL1bDeFlags IntFlag for DE packet-level quality bits.
imap_processing/cdf/config/imap_hi_variable_attrs.yaml	Adds attribute definitions for hi_de_esa_step_met and hi_de_ccsds_qf.
imap_processing/tests/hi/test_hi_l1b.py	Updates dataset variable count expectations and adds unit tests for the new functions.

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[lacoak21]

I would think that if there were no valid events you would want everything flagged? Not with ImapHiL1bDeFlags.PACKET_FULL but another one?

[subagonsouth]

I could add another flag to indicate an empty packet but currently, the only flag I have defined indicates that the CCSDS packet contained the maximum number of events. You are correct that a packet having no packets probably indicates a problem but that may be caught elsewhere.