Replace Perl binding cleanup with V

[antono3]

Summary

• replace the combined Perl binding postprocessor with a V-native implementation
• move variant configuration and verification from Perl-backed shell scripts to .vsh scripts
• make the C translation workaround V-native and remove stale Perl scratch ignores
• run the cleanup self-test in the always-reported demo workflow

Compatibility

The new cleaner was compared against freshly translated cimgui/cimplot inputs. Its ImGui and ImPlot outputs are byte-for-byte identical to the previous implementation after accounting for the implementation filename in the generated non-regression note.

Verification

• v run cleanup_imgui_implot.vsh --self-test
• v vet cleanup_imgui_implot.vsh scripts/configure_variant.vsh scripts/check_upstream_variant.vsh generate.vsh
• v run scripts/check_upstream_variant.vsh
• v run generate.vsh (translation, both cleanup passes, formatting, and native shared-library build)
• docking ABI configuration round-trip through standard and back with no residual diff
• golden cleanup comparison for both generated bindings
• memory-guarded cleanup run: ImGui 147 MiB peak / 0.42 s; ImPlot 83 MiB peak / 0.27 s