Implement harmonize_fct()

[jonthegeek]

Closes #3.

[Copilot]

Pull Request Overview

Implements factor harmonization functionality and refactors the factor specification away from an S7 class to a lightweight list-based spec.

• Adds harmonize_fct() with lookup support and tests.
• Replaces S7-based hrmn_fct spec with list-based hrmn_fct_spec and updates tests/docs.
• Removes S7 dependency; adds fastmatch, rlang, and stbl dependencies.

Reviewed Changes

Copilot reviewed 13 out of 13 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
tests/testthat/test-specify_fct.R	Updates tests to reflect new list-based spec class and accessor ($ instead of @).
tests/testthat/test-harmonize_fct.R	Adds comprehensive tests for harmonize_fct() behavior (empty input, lookup, NA handling, spec enforcement).
R/specify_fct.R	Refactors specify_fct() to return a list-based spec with new class vector.
R/harmonize_fct.R	Introduces harmonize_fct() and internal .apply_fct_lookup().
R/aaa-shared_params.R	Adds shared parameter documentation for reuse.
R/hrmn-package.R	Imports fastmatch %fin% operator.
man/*.Rd	Updates and adds documentation for new/modified functions.
NAMESPACE	Exports harmonize_fct() and imports %fin%; removes S7 import.
DESCRIPTION	Bumps version; updates Imports (removes S7, adds fastmatch, rlang, stbl).
R/zzz.R	Removes obsolete S7-related helper.

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