test+docs: spec coverage for migratus-enablement fixes; list migratus

Adds spec/conformance coverage for everything landed enabling migratus:
- conformance corpus (runs interpret/compile/self-host): def 3-arg docstring,
  def/defn ^{:map} name meta, defmacro arity-clause + docstring, defmulti
  docstring, assoc-nil/assoc-in real maps, try multi-body + finally-on-success,
  current-ns restore after a caught throw, cross-ns methods visibility.
- spec suites: host-interop (exception ctors, Character/Thread/Long, Timestamp/
  SimpleDateFormat, java.io.File model + File-aware file-seq, clojure.tools.logging),
  regex (Pattern statics + MULTILINE + quote, String .matches/.replaceAll/
  .replaceFirst), maps (assoc on nil), multimethods (defmulti docstring +
  value-based methods/get-method), macros (defmacro arity-clause + name meta).

Rewrote clojure.tools.logging/spy as a single variadic arity (jolt defmacro
takes only the first clause of a multi-arity macro — jolt-q8l).

docs/libraries.md: add migratus and the next.jdbc compatibility layer, with the
janet-lang/sqlite3 int64 caveat for 14-digit timestamp ids.

Full gate green; conformance 350/350 x3 modes.

test/spec/multimethods-spec.janet

@@ -54,3 +54,17 @@
    "(do (defmulti pm5 identity) (defmethod pm5 :a [x] 1) (defmethod pm5 :b [x] 2) (prefer-method pm5 :a :b) (contains? (get (prefers pm5) :a) :b))"]
   ["exact match needs no preference" ":exact"
    "(do (derive :t/sq :t/rect) (defmulti pm6 identity) (defmethod pm6 :t/sq [x] :exact) (defmethod pm6 :t/rect [x] :parent) (pm6 :t/sq))"])
+
+# defmulti drops a leading docstring/attr-map (jolt-es4 — it used to be taken as
+# the dispatch fn). methods/get-method take the multimethod VALUE and recover
+# the table, so a bare multifn ref works even when defmethods live elsewhere
+# (jolt-9pu).
+(defspec "multimethods / docstring & value-based table ops"
+  ["defmulti docstring"   "\"A\""
+   "(do (defmulti gd \"the dispatcher\" identity) (defmethod gd :a [_] \"A\") (gd :a))"]
+  ["defmulti doc+default" "\"d\""
+   "(do (defmulti gx \"doc\" identity) (defmethod gx :default [_] \"d\") (gx :anything))"]
+  ["methods on value"     "2"
+   "(do (defmulti gm identity) (defmethod gm 1 [_] :one) (defmethod gm 2 [_] :two) (count (methods gm)))"]
+  ["get-method on value"  "true"
+   "(do (defmulti gg identity) (defmethod gg :a [_] :x) (fn? (get-method gg :a)))"])