fix(clean): avoid arithmetic error when no unavailable simulators exist (#742)

[sebastianbreguel]

Fixes #742. Regression from #714.

grep -c exits 1 on zero matches, so the || echo \"0\" fallback fires even when grep already printed "0", producing "0\n0" and breaking the [[ -gt ]] comparison in clean_xcode_tools.

Switches to the awk '/pattern/ { count++ } END { print count+0 }' pattern already used in lib/clean/dev.sh:778,818 — exit-code independent, always emits a single integer. Keeps a numeric sanity regex as a belt-and-suspenders guard.

Changes

• lib/clean/app_caches.sh: replace grep -cE ... || echo "0" with command awk counter + numeric validation.
• tests/clean_app_caches.bats: add two regression tests (zero unavailable sims + populated DRY_RUN path).

Verification

bats tests/clean_app_caches.bats -f "simulator|Xcode"
ok 1 clean_xcode_tools skips derived data when Xcode running
ok 2 clean_xcode_tools cleans documentation caches when Xcode is not running
ok 3 clean_xcode_tools handles zero unavailable simulators without syntax error
ok 4 clean_xcode_tools reports unavailable simulators when present

Credit to @yetval for identifying the exact root cause in the issue thread.

[tw93]

@sebastianbreguel thanks for fixing the simulator count arithmetic error, merged and will be in the next release.