SpecsIo: OS-created temp directory and OS cache folder helpers

[lm-sousa]

Adds two helpers to SpecsIo so callers stop hand-rolling temporary directory names (UUID concat, nanoTime+threadId, fixed cwd-relative names) and stop hardcoding OS cache conventions:

• SpecsIo.createTempDirectory(prefix): unique directory allocated by the OS under the user temp folder (/tmp/tmp_<user> on Linux), registered for deletion on exit as a backstop; owners are expected to delete it when their lifecycle ends
• SpecsIo.getOsCacheFolder(): user-level cache folder following OS conventions ($XDG_CACHE_HOME or ~/.cache, ~/Library/Caches, %LOCALAPPDATA%), created if missing
• SpecsSystem.isMac()

Consumed by specs-feup/clava (stacked work): the parser/weaver/tester now use OS-allocated folders with per-instance ownership (clava #251, #264, #248, #249) and the clang-dumper cache root is unified on getOsCacheFolder() (clava #250).

Note: the branch also carries the earlier jOptions GuiHelper-coupling removal commit (5fafd1ae).

Tests: new cases in SpecsIoTest (uniqueness, OS temp parent, cache folder stability).

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[lm-sousa]

Superseded: this work moves to a dedicated dir-fixes branch stacked on clava-simplification, to keep the simplification PR untouched.