Refactor box base XPath

[radbasa]

Refer to PR #179

Separate pull request to isolate changes.

Description

• The detection for / to identify modules, and no / to identify packages have been moved to the functions.
• box_module_base_path() and box_package_base_path() are now replaced by the common box_base_xpath().
• All functions that refer to box_*_base_path() have been modified to use box_base_xpath().
• Legacy linters with hard-coded box base xpath have also been modified to reference box_base_xpath().
• New unit test cases added for box_unique_names_linter.
• Unit tests for all other linters are unmodified.
• Regression tests pass.

Definition of Done

• The change is thoroughly documented.
• The CI passes (R CMD check, linter, unit tests, spelling).
• Any generated files have been updated (e.g. .Rd files with roxygen2::roxygenise())

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 97.10%. Comparing base (3231b1b) to head (d0da497).

Additional details and impacted files

@@                        Coverage Diff                        @@
##           177-unique-attached-object-names     #180   +/-   ##
=================================================================
  Coverage                             97.10%   97.10%           
=================================================================
  Files                                    25       25           
  Lines                                  1242     1243    +1     
=================================================================
+ Hits                                   1206     1207    +1     
  Misses                                   36       36           

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