chore: remove deprecated arguments (input_zip, dict) from zi_crosswalk()

[chris-prener]

Problem

zi_crosswalk() carries two deprecated arguments — input_zip and dict — that have been superseded by input_var and zip_source/year respectively. The deprecation warnings promise removal "in early 2027."

Proposal

After the deprecation grace period expires (early 2027), remove the deprecated arguments and their handling code:

1. Remove input_zip parameter and its migration shim
2. Remove dict parameter and its migration shim
3. Update roxygen2 documentation to drop the deprecated @param entries
4. Update any vignettes or examples still referencing old arguments
5. Bump package version appropriately (minor or major per policy)

Acceptance criteria

• input_zip and dict arguments fully removed from zi_crosswalk() signature
• Deprecation handling code removed from function body
• Roxygen2 docs updated — no references to removed arguments
• R CMD check passes with 0 errors, 0 warnings, 0 notes
• CHANGELOG entry under breaking changes
• Package version bumped appropriately

Timing

Do not action before January 2027. The deprecation notice promises "early 2027" removal.

Codebase Context

• R/zi_crosswalk.R lines 53–55 (roxygen), 98–119 (deprecation shims)

[chris-prener]

Implementation plan

Status: Blocked

Constraint

⚠️ Do not implement before January 2027. The deprecation notice in the code promises users removal "in early 2027." Implementing early would break the deprecation contract.

Steps (for execution in early 2027)

1. Remove input_zip parameter from zi_crosswalk() signature (line 94)

   • Remove from function(... input_zip, ...) formals

2. Remove dict parameter from zi_crosswalk() signature (line 94)

   • Remove from function(... dict = NULL) formals

3. Remove deprecation shim code (lines 97–120 in R/zi_crosswalk.R)

   • Delete the if (!is.null(dict)) block (lines 97–113)
   • Delete the if (!missing(input_zip)) block (lines 115–120)

4. Update roxygen2 documentation

   • Remove @param input_zip (line 53–54)
   • Remove @param dict (lines 55–56)
   • Run devtools::document() to regenerate NAMESPACE/man files

5. Check for references elsewhere

   • Search vignettes, README, tests for input_zip or dict usage
   • Update or remove any remaining references

6. Add CHANGELOG entry

   • Under "Breaking Changes": document removal of deprecated arguments

7. Bump version (coordinate with release version decision)

   • At minimum a minor bump; consider major if this is the only breaking change in the release

8. Run R CMD check — 0 errors, 0 warnings, 0 notes

Estimated scope

~30 lines removed from R/zi_crosswalk.R, minor doc updates. Low complexity, but the timing constraint is critical.