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/exceptions-spec.janet

@@ -0,0 +1,28 @@
+# Specification: exceptions — try/catch/finally, throw, ex-info.
+(use ../support/harness)
+
+(defspec "exceptions / try-catch"
+  ["catch :default"      ":caught"
+   "(try (throw (ex-info \"boom\" {})) (catch :default e :caught))"]
+  ["catch by class"      ":caught"
+   "(try (throw (ex-info \"boom\" {})) (catch Exception e :caught))"]
+  ["catch binds error"   "\"boom\""
+   "(try (throw (ex-info \"boom\" {})) (catch :default e (ex-message e)))"]
+  ["no throw -> body"    "1"
+   "(try 1 (catch :default e :caught))"]
+  ["finally runs on ok"  "2"
+   "(let [a (atom 0)] (try 2 (finally (reset! a 9))) )"]
+  ["finally runs on throw" "9"
+   "(let [a (atom 0)] (try (throw (ex-info \"x\" {})) (catch :default e nil) (finally (reset! a 9))) @a)"]
+  ["catch value of body" "5"
+   "(try (+ 2 3) (catch :default e 0))"])
+
+(defspec "exceptions / ex-info"
+  ["ex-message"          "\"oops\""  "(ex-message (ex-info \"oops\" {}))"]
+  ["ex-data"             "{:k 1}"    "(ex-data (ex-info \"oops\" {:k 1}))"]
+  ["ex-data via catch"   "{:code 42}"
+   "(try (throw (ex-info \"e\" {:code 42})) (catch :default e (ex-data e)))"]
+  ["ex-cause"            "true"
+   "(let [c (ex-info \"root\" {})] (= c (ex-cause (ex-info \"outer\" {} c))))"]
+  ["propagates to outer"  "\"inner\""
+   "(try (try (throw (ex-info \"inner\" {})) (finally nil)) (catch :default e (ex-message e)))"])