Fix replacement filters default value and ensure plain dict conversion

[Copilot]

The override_filters field in replace_obs_filters was defaulting to an empty dict {} instead of an empty list [], and values retrieved from the template dictionary (potentially wxflow attrdicts) were not being converted to plain Python dicts.

Changes

• Added to_plain_dict() utility function: Recursively converts dict-like objects (e.g., wxflow attrdict) and nested structures to plain Python dicts
• Changed default value: override_filters now defaults to [] instead of {}
• Applied conversion: All retrieved override_filters values are converted via to_plain_dict() to ensure consistent plain dict types throughout nested structures

# Before
new_filters = replace_obs_filters_dict.get('override_filters', {})

# After
new_filters = replace_obs_filters_dict.get('override_filters', [])
new_filters = to_plain_dict(new_filters)

The conversion handles arbitrary nesting depth and preserves list structures containing dicts.

Original prompt

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This section details on the original issue you should resolve

<issue_title>Replacement filters should be a list + make plain dict</issue_title>
<issue_description>

jcb/src/jcb/renderer.py

Line 261 in 62d6b44

new_filters = replace_obs_filters_dict.get('override_filters', {})

This line should end with [] not {} and also the list of dicts needs to be forced to be plain, vanilla dicts and not wxflow attrdict. Maybe?</issue_description>

Comments on the Issue (you are @copilot in this section)

@CoryMartin-NOAA Needs to nest in and convert to plain dicts also... perhaps something else is going on.??

• Fixes Replacement filters should be a list + make plain dict #35

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