Add test for AbsolutePath.deleteRecursively on missing path

[rochala]

Follow-up to #89.

The fix in #89 makes AbsolutePath.deleteRecursively no-op when the target path does not exist (previously Files.walk threw NoSuchFileException). The fix shipped without a regression test.

What to cover

• deleteRecursively on a non-existent path → no exception, no-op.
• deleteRecursively on an existing directory tree (nested files/dirs) → fully removed.
• (optional) deleteRecursively on a single file → removed.

Notes

• Lives in sls/src/org/scala/abusers/sls/paths.scala.
• Use a temp dir fixture; Weaver-Cats SimpleIOSuite per repo conventions.