fix: resolve class/package name conflicts on case-insensitive filesystems (PR #2828)

* Fix: resolve class/package name conflicts on case-insensitive filesystems

**RenameVisitor**
- Added package-level conflict detection for case-insensitive filesystems:
  when two packages differ only by case (e.g. com.Example vs com.example),
  rename the conflicting one and loop until the new name is also unique
- Added class-level conflict detection (same pattern): when two classes in
  the same package differ only by case (e.g. Sink vs sink), rename the
  conflicting one to prevent file overwrite on Windows export

**Tests**
- Added TestCaseSensitivePkgChecks: verifies package rename when packages
  differ only by case; fixed smali data (2.smali changed Bar→Foo to create
  a genuine path conflict under case-insensitive FS)
- Added TestCaseSensitiveClassInPkgChecks + smali fixtures: verifies class
  rename when two classes in a named package differ only by case
  (com.example.User vs com.example.user)

* Apply suggestions from code review

Co-authored-by: skylot <118523+skylot@users.noreply.github.com>

* Apply suggestions from code review

Co-authored-by: skylot <118523+skylot@users.noreply.github.com>

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Co-authored-by: john <johnwsa@qq.com>
Co-authored-by: skylot <118523+skylot@users.noreply.github.com>