Fix box_usage_linter working dir resolution; add R6 inheritance support

[dereckmezquita]

Fixes #150, #157, and #188.

box_usage_linter — working dir fix

box_usage_linter() didn't set the working directory before resolving module exports, so lint_dir() from a parent directory produced false positives on module$function() calls.

Applied the same withr::with_dir(get_module_working_dir(...)) pattern that the other module linters already use. 3 lines changed.

r6_usage_linter — inheritance

r6_usage_linter() ignored the inherit paramater entirely, flagging all inherited method calls as invalid.

Added get_r6_inherited_components() which resolves parent class components from:

• Same file (including multi-level chains)
• Other modules via box::use() (alias$Class and [Class] patterns)
• Installed packages (via R6ClassGenerator introspection)

Includes cycle protection. Switched to file-level linting and scoped XPaths with .// to handle mutliple R6 classes per file.

Tests

• 12 new tests, 8 fixture files
• 444 pass, 0 fail
• R CMD check: 0 errors, 0 warnings, 0 notes

[dereckmezquita]

box_usage_linter fixes

I wrapped the 3 module resolution calls in with::with_dir I saw this somewhere else in the code base and this resolves the issue - the box_usage_linter module was the only one not using this pattern.

r6_usage_linter new features

I use R6 classes in my codebase extensively and chained inheritance as such this is a feature I needed, I included it in this same PR.

To add support for this I switched from expression level to file level linting this is so that the full XML tree can be available for look ups across classes. I changed XPaths from // to .// to scope searches to the current R6 class node; in order to avoid cross class contamination when multiple classes are in a single module. I then iterate on all R6 classes inn the file with lapply.

I added get_r6_inherited_components to parse the inherit argument. It will:

1. Look in the current file first.
2. Look in box::use
3. Allow for $ accessor.
4. Allow for package classes.
5. Support resolving classes across modules.