test: fold cljs ports into spec; add exceptions spec + gap coverage

Mine the cljs port batteries into the spec layer and delete them (their behavior
is covered by spec; the unique functions they exercised are now specced).
Removed test/integration/ports/ entirely.

New/expanded spec coverage from the mining:
- spec/exceptions-spec: try/catch/finally, throw, ex-info/ex-message/ex-data/ex-cause
- doto, pr-str, keyword/symbol constructors, atom?, dynamic var binding

Two rare edges filed (jolt-...): rethrow of a caught ex-info re-wraps it; var-set
on a dynamic var inside binding no-ops. Core try/catch/ex-info and binding work.

Test layout is now spec (22 files, ~677 cases) / integration / unit / support.
conformance 218/218, jpm test green.

test/spec/control-flow-spec.janet

@@ -59,4 +59,5 @@
   ["some-> nil stops"   "nil"    "(some-> nil inc)"]
   ["some->>"            "[2 3]"  "(some->> [1 2] (map inc))"]
   ["cond->"             "2"      "(cond-> 1 true inc false inc)"]
-  ["cond->>"            "[1 2]"  "(cond->> [2] true (cons 1))"])
+  ["cond->>"            "[1 2]"  "(cond->> [2] true (cons 1))"]
+  ["doto returns subject" "5"    "(let [a (doto (atom 0) (reset! 5))] @a)"])