Rebuild tag-based subdecks when dissolving block exam subdecks

[RisingOrange]

This PR improves compatibility between block exam subdecks and subdeck tag features by ensuring notes return to their proper tag-based subdecks when a block exam subdeck is dissolved.

Related issues

• Closes # (add issue number if applicable)

Proposed changes

1. Refresh tag-based subdecks on subdeck dissolution

• When dissolving a block exam subdeck from an AnkiHub deck with subdecks enabled, notes are now redistributed to their appropriate tag-based subdecks
• Previously, notes would stay in the root deck after dissolution, breaking the subdeck tag organization
• This ensures the subdeck tag feature continues working correctly after temporary block exam subdecks are removed

2. Rename function for clarity

• Renames move_subdeck_to_main_deck() → dissolve_block_exam_subdeck()
• The new name better reflects the actual behavior: dissolving the subdeck structure and redistributing notes appropriately
• More accurate since notes don't necessarily end up in the main deck - they may be redistributed to tag-based subdecks

3. Update tests and documentation

• Adds test coverage for subdeck rebuilding with test_dissolve_subdeck_with_subdecks_enabled
• Updates existing tests to properly verify both scenarios:
  • Non-AnkiHub decks: notes stay in root deck
  • AnkiHub decks with subdecks enabled: notes are redistributed to tag-based subdecks
• Updated docstring to clearly explain the two-step redistribution process

How to reproduce

Testing subdeck tag compatibility (main feature):

• Set up an AnkiHub deck subdecks enabled and a note with a subdeck tag
  • Add AnkiHub_Subdeck::AnKing_Overhaul_for_Step_1_&_2::foo to a note
  • Use Anki Browser -> AnkiHub -> Rebuild subdecks and move cards into subdecks
  • You can unsuspend the card of the note so that you can see the "1" new note next to the deck name
    
• Create a block exam subdeck and move the note with the subdeck tag into it
  
• Remove the tag-based deck ("foo")
  
• Merge the block exam subdeck into the parent deck
• Expected: The tag-based deck is recreated, and the note is moved back into it
  

Testing the unit tests:

xvfb-run python -m pytest tests/addon/test_unit.py::TestDissolveBlockExamSubdeck -v --show-capture=no --disable-warnings -n 0

All three test cases should pass:

• test_dissolve_block_exam_subdeck_success - Basic dissolution without subdeck rebuilding
• test_dissolve_subdeck_with_subdecks_enabled - Dissolution with subdeck rebuilding for AnkiHub decks (key test)
• test_dissolve_subdeck_not_found - Error handling when subdeck doesn't exist

Screenshots and videos

N/A - The feature works behind the scenes to maintain subdeck tag organization.

Further comments

Why this matters:

Block exam subdecks and subdeck tags serve different purposes:

• Block exam subdecks: Local, user-specific temporary organization for exam preparation
• Subdeck tags: Shared across all deck subscribers, part of the deck's content organization

Without this change, dissolving a block exam subdeck would leave notes orphaned in the main deck, breaking the tag-based subdeck organization. This PR ensures the two features work together properly - block exam subdecks can be created and dissolved without disrupting the underlying tag-based subdeck structure.