Refactor: Move all deduplication functions from library to CLI

[Copilot]

Problem

The bibfmt library contained several functions that belonged more naturally in the bibdedup CLI tool rather than in the library, as they either performed I/O operations or implemented workflow logic specific to the CLI tool. This:

1. Mixed business logic with user interaction
2. Made the library unsuitable for programmatic use in non-interactive contexts
3. Violated separation of concerns between library and application layers

Solution

This PR refactors the deduplication functionality by:

Moved to CLI (bibfmt/bin/bibdedup.ml):

• deduplicate_entries - orchestrates the deduplication workflow with progress output
• resolve_conflicts - interactively prompts users to resolve field conflicts
• display_conflict - displays conflict information to users
• prompt_user_choice - reads user input for conflict resolution
• merge_entries_non_interactive - merges duplicate entries (workflow logic)

Kept in Library (bibfmt/lib/bibtex.ml):

• find_duplicate_groups - pure function that identifies duplicates for programmatic use
• Helper functions: string_of_field_value, make_field
• Type definitions: field_conflict, duplicate_group

Updated Public Interface (bibfmt/lib/bibtex.mli):

• Removed deduplicate_entries and merge_entries_non_interactive from public API
• Exposed string_of_field_value and make_field helpers (needed by CLI)

Benefits

• Cleaner architecture: Library now provides only core duplicate detection functionality
• Better separation of concerns: All deduplication workflow logic is confined to the CLI layer
• No duplicate code: All deduplication and merging logic lives in one place
• Maintains functionality: bibdedup CLI works exactly as before
• Improved reusability: Library's find_duplicate_groups can be used programmatically for duplicate detection

Testing

While I don't have the OCaml toolchain set up to run tests, the refactoring:

• Preserves all existing functionality by moving code without changing logic
• Uses the same algorithms and data structures as before
• Only changes where the code lives (library vs CLI)

The bibdedup CLI should behave identically to before, and the library now provides a cleaner API focused on duplicate detection rather than complete deduplication workflows.

Closes #[issue-number]

Original prompt

On bibtex.ml, resolve_conflicts, merge_entries and deduplicate_entries are all functions that require interaction or IO to inform the user. They belong better inside the bibdedup.ml cli tool rather than here in the library. Make a PR to move the code appropriately, clean up unnecessary duplication

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[mseri]

@copilot move also merge_entries_non_interactive

[Copilot]

@copilot move also merge_entries_non_interactive

Done. Moved merge_entries_non_interactive to bibdedup.ml in commit 8dd3e89.