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/predicates-spec.janet

@@ -47,7 +47,11 @@
   ["name of keyword"    "\"a\""  "(name :a)"]
   ["name of qualified"  "\"b\""  "(name :a/b)"]
   ["namespace"          "\"a\""  "(namespace :a/b)"]
-  ["namespace simple"   "nil"    "(namespace :a)"])
+  ["namespace simple"   "nil"    "(namespace :a)"]
+  ["keyword constructor" ":foo"  "(keyword \"foo\")"]
+  ["keyword ns + name"  ":a/b"   "(keyword \"a\" \"b\")"]
+  ["symbol constructor" "(quote x)" "(symbol \"x\")"]
+  ["name of string"     "\"s\""  "(name \"s\")"])
 
 (defspec "predicates / equality & identity"
   ["= same"             "true"   "(= 1 1)"]