Unify resolver return types for consistent CLI pipeline behavior

[Copilot]

Resolvers in Pedal were returning inconsistent data types, causing CLI pipelines to break and requiring brittle workarounds. This PR standardizes all resolver return types to use a unified dictionary format.

Problem

Previously, different resolvers returned different data types:

• simple.resolve() and full.resolve() returned FinalFeedback objects
• statistics.resolve() returned a dictionary with {'final': dict, 'considered': list}
• silent.resolve() returned an empty string
• sectional.resolve() returned a dictionary with group mappings

This inconsistency required workaround code like:

def to_json(self):
    resolution = ({'final': self.resolution.to_json()}
                  if isinstance(self.resolution, FinalFeedback)
                  else self.resolution.copy() 
                  if self.resolution else {})

Solution

All main resolvers now consistently return the unified format:

{
    'final': final_feedback_dict,      # The chosen feedback as JSON
    'considered': [feedback_dicts]     # All considered feedback as JSON
}

This format:

• ✅ Provides comprehensive information for analysis and debugging
• ✅ Eliminates the need for type-checking workarounds
• ✅ Supports the full range of capabilities mentioned in the original issue
• ✅ Maintains backwards compatibility through consistent JSON structure

Changes Made

• Updated resolvers: Modified simple.py, full.py, and silent.py to return the unified format
• Removed workarounds: Eliminated isinstance checks in CLI code
• Fixed environments: Updated terminal and standard environments to handle the new format
• Updated tests: Modified resolver tests to work with the new dictionary format
• Validated CLI: Ensured all CLI commands work correctly with the changes

Testing

All CLI functionality has been validated:

• pedal grade simple_test.py submissions/correct.py --environment terminal ✅
• pedal sandbox submissions/correct.py ✅
• pedal --help ✅
• Package imports and resolver tests ✅

The sectional resolver maintains its existing format since it handles multiple sections differently, but the main single-result resolvers are now fully unified.

Fixes #140.

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